referring now to the drawings and first to fig1 - 21 which shows a first non - limiting embodiment of a blood collection device 10 according to the invention . the device 10 includes a generally cylindrical outer sleeve or outer body member 20 which includes a proximal end 20 a configured to allow an external needle n of a double - ended needle member or holder 30 to pass therethrough , and a distal end 20 b which can be closed off by a cap 50 . an inner flange if is arranged at the proximal end 20 a . the needle holder 30 has an outer circumferential surface ocs ( see fig1 ) which frictionally engages with an inner circumferential surface ics ( see fig1 and 18 ) of a proximal end of an inner sleeve 40 . the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 10 also includes a spring 60 which functions to move the needle holder 30 distally when the outer circumferential surface ocs of the needle holder 30 is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 40 . as is evident from fig1 , once a user moves the cap 50 to the closed position , the sleeve 40 is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 30 no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 40 . the spring 60 is then free to move the needle holder 30 within the sleeve 40 in a distal direction which ensures that the needle holder 30 is fully and safely arranged within the device 10 . the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 40 from the needle holder 30 ( see fig1 ) functions as follows . the sleeve 40 is prevented from moving axially backwards within the body 20 by two oppositely arranged projections p , but is biased towards this direction by the spring 60 which fig1 is substantially fully compressed . the projections p also function as static pivot points and allow the generally half - circular or arc - shaped sections 40 a and 40 b of the sleeve 40 to pivot relative each other . thus , as shown in fig1 , when the distal ends of the generally half - circular or arc - shaped sections 40 a and 40 b of the sleeve 40 are moved towards each other , the proximal ends of the generally half - circular or arc - shaped sections 40 a and 40 b of the sleeve 40 are moved away from each other . as a result , the two oppositely arranged proximal slots ps widen while the two oppositely arranged distal slots ds narrow . as is shown in fig1 , this pivot movement is caused when the user moves the cap 50 to the closed position , and more specifically , when the inner tapered surfaces tpe of the cap 50 engage with tapered surfaces tde of the sleeve 40 and force the tapered surfaces tde of the sleeve 40 inwardly . with reference to fig1 and 12 , when the user moves the cap 50 to the closed position , the inner tapered surfaces tpe of the cap 50 engage with tapered surfaces tde of the sleeve 40 and force the tapered surfaces tde of the sleeve 40 inwardly . this , however , also causes the sleeve 40 to move a small amount in the distal direction , and this movement is not prevented by the projections p . instead , this movement is limited by the biasing force of the spring 60 and by contact between a front - facing surface of the holder 30 and a rear - facing surface of the inner flange if of the body 20 . as is shown in fig1 , when the user moves the cap 50 to the closed position shown in fig1 , the pivoting movement of the sections 40 a and 40 b automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 30 and the sleeve 40 , the disengagement of these surfaces leaves the holder 30 free to move axially distally . furthermore , because the spring 60 maintains a biasing force against the holder 30 , when the engagement is released , the spring 60 will automatically expand axially and force the holder 30 to move distally within the sleeve 40 . thus , in turn , results in the needle n being retracted into the sleeve 40 and positions it safely within the body 20 . the device 10 shown in fig1 is now rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 10 . with reference to fig1 - 19 , it can be seen that the sleeve 40 and the needle holder 30 constitute a sub - assembly with the generally half - circular or arc - shaped sections 40 a and 40 b of the sleeve 40 assuming a generally cylindrical shape . the two oppositely arranged connecting portions cp function as the only mechanism connecting together the arc - shaped sections 40 a and 40 b of the sleeve 40 . as such , when the distal ends of these members 40 a and 40 b are moved towards each other , the connecting portions cp become deflected and / or slightly elastically deformed thereby allowing the proximal ends of the generally half - circular or arc - shaped sections 40 a and 40 b of the sleeve 40 to move away from each other . however , in the relaxed shown in fig1 , the connecting portions cp ensure that the surfaces osc and ics remain in engagement . in order to assemble the sub - assembly shown in fig1 , one need only move the tapered surfaces tde of the members 40 a and 40 b towards each other to cause a widening of the slots ps ( and simultaneously a narrowing of the slot ds ), insert the holder 30 within the proximal end of the sleeve 40 , and then remove the force applied to the surfaces tde allowing the sleeve 40 to again assume a generally cylindrical shape shown in fig1 . of course , proper insertion and connection of the holder 30 requires ensuring that the projections cpp , epp ( see fig1 and 17 ) are aligned with the circumferential groove g of the sleeve 40 ( see fig1 ). the sub - assembly shown in fig1 can be slid into the distal end of the body 20 in a relatively easy manner because the two integrally formed oppositely arranged projections p have a tapered inward facing surface which allows the connecting portions cp to slide over the projections p . the projections p also serve to align and / or guide the proper insertion movement of the sub - assembly shown in fig1 as follows . upon insertion of the sleeve 40 into the distal end of body 20 , the user will align the proximal slots ps of the sleeve 40 with the projections p and then move the sleeve 40 axially in the proximal direction . once the connecting portions cp of the sleeve 40 reach the projections p , the tapered surfaces of the projections p allow these portions cp to pass over the projections p until they pass the projections p and snap outwardly and assume the final position shown in fig1 . at this point , the rear - facing surface of the portions cp will abut the forward facing surface css ( see fig2 ) of the projections p . the spring 60 can , of course , be installed inside the body 20 in the same way as , e . g ., the prior art device shown in fig1 - 10 , and is preferably installed in the body 20 prior to or simultaneously with the insertion of the sub - assembly shown in fig1 . with reference to fig1 - 17 , it can be seen that the needle holder 30 constitutes a sub - assembly having , in the case of fig1 , four equally angularly spaced circular projections cpp which are sized to engage or extend into the groove g of the sleeve 40 . of course , the invention also contemplates using as few as two oppositely arranged projections cpp . furthermore , the projections cpp need not be circular and / or rounded and can be any shape ( e . g ., square , triangular , oval , polygonal , etc .) which securely and releasably engages with the groove g . furthermore , the groove g need not correspond in shape to that of the projections cpp , and can similarly have any shape which securely and releasably engages with the projections cpp . by way of non - limiting example fig1 shows four equally angularly spaced elongated projections epp which are sized to engage or extend into the groove g of the sleeve 40 . again , the invention also contemplates using as few as two oppositely arranged projections epp . furthermore , the projections epp need not be rounded and can be any shape ( e . g ., square , triangular , oval , polygonal , etc .) which securely and releasably engages with the groove g . the invention also contemplates other mechanisms for providing a releasable engagement between the surfaces ocs and ics . still further , instead of merely utilizing a single groove g and a single set of projections cpp , epp , the invention also contemplates using two or more axially spaced grooves g and two or more axially spaced sets of projections cpp , epp . fig2 shows a second non - limiting embodiment of a blood collection device 10 ′ according to the invention . the device 10 ′ is shown in the used or post use position . as was the case in the previous embodiment , the device 10 ′ includes a generally cylindrical outer sleeve or outer body member 20 which includes a proximal end 20 a configured to allow an external needle n of a double - ended needle member or holder 30 ″ to pass therethrough , and a distal end 20 b which can be closed off by a cap 50 . an inner flange if is arranged at the proximal end 20 a . the needle holder 30 ″ has an outer circumferential surface ocs which frictionally engages with an inner circumferential surface ics of a proximal end of an inner sleeve 40 ′. the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 10 ′ also includes a spring 60 which functions to move the needle holder 30 ″ distally when the outer circumferential surface ocs of the needle holder 30 ″ is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 40 ′. as was the case in the previous embodiment , once a user moves the cap 50 to the closed position , the sleeve 40 ′ is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 30 ″ no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 40 ′. the spring 60 is then free to move the needle holder 30 ″ within the sleeve 40 ′ in a distal direction which ensures that the needle holder 30 ″ is fully and safely arranged within the device 10 ′. this is shown in fig2 . the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 40 ′ from the needle holder 30 ″ functions as follows . the sleeve 40 ′ is prevented from moving axially backwards within the body 20 by two oppositely arranged projections p ( not shown , but similar to the previous embodiment ), but is biased towards this direction by the spring 60 . as in the previous embodiment , the projections p also function as static pivot points and allow the generally half - circular or arc - shaped sections 40 ′ a and 40 ′ b of the sleeve 40 ′ to pivot relative each other . thus , as shown in fig2 , when the distal ends of the generally half - circular or arc - shaped sections 40 ′ a and 40 ′ b of the sleeve 40 ′ are moved towards each other , the proximal ends of the generally half - circular or arc - shaped sections 40 ′ a and 40 ′ b of the sleeve 40 ′ are moved away from each other . as a result , the two oppositely arranged proximal slots ps widen while the two oppositely arranged distal slots ds narrow . as is shown in fig2 , this pivot movement is caused when the user moves the cap 50 to the closed position , and more specifically , when the inner tapered surfaces tpe of the cap 50 engage with tapered surfaces tde of the sleeve 40 ′ and force the tapered surfaces tde of the sleeve 40 ′ inwardly . as is evident from fig2 , when the user moves the cap 50 to the closed position shown in fig2 , the pivoting movement of the sections 40 ′ a and 40 ′ b automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 30 ″ and the sleeve 40 ′, the disengagement of the surfaces ics and ocs leaves the holder 30 ″ free to move axially in the distal direction . furthermore , because the spring 60 maintains a biasing force against the holder 30 ″, when the engagement is released , the spring 60 will automatically expand axially and force the holder 30 ″ to move distally within the sleeve 40 ′. thus , in turn , results in the needle n being retracted into the sleeve 40 ′ and positions it safely within the body 20 . the device 10 ′ shown in fig2 is now rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 10 ′. in the embodiment shown in fig2 , the needle holder 30 ″ has two equally angularly spaced circular indentations or blind recesses crr which are sized to receive therein and engage with corresponding projections cpr of the sleeve 40 ′. of course , the invention also contemplates using more than two oppositely arranged projections cpr and recesses crr . additionally , it is possible , and even preferable from a manufacturing or assembly standpoint , to utilize a continuous or circumferential groove in place of the two recesses crr . furthermore , the projections cpr need not be circular and / or rounded and can be any shape ( e . g ., square , triangular , oval , polygonal , etc .) which securely and releasably engages with the recesses crr . furthermore , the recess crr need not correspond in shape to that of the projections cpr , and can similarly have any shape which securely and releasably engages with the projections cpr . other than the different configurations shown in fig2 regarding the surfaces ics and ocs , the embodiment shown in fig2 is substantially similar to that of fig1 - 21 . fig2 shows another embodiment of an inner sleeve 40 ″ which can be used , e . g ., in the embodiment of fig1 - 21 in place of the sleeve 40 . the sleeve 40 ″ is similar to sleeve 40 except that the connecting portions cp ′ in the instant embodiment is formed by a sideways disconnectable joint formed by circular projection bp and a socket recess sr which forms a pivot bearing for the projection bp . the advantage of this joint cp ′ system is that it allows arc - shaped members 40 ″ a and 40 ″ b forming the sleeve 40 ″ to pivot relative to each other more easily , i . e ., when the cap 50 is moved to the closed position and the tapered surfaces tpe engage the tapered surfaces tde . another advantage is that the arc - shaped members 40 ″ a and 40 ″ b forming the sleeve 40 ″ can be formed separately and allows the sleeve 40 ″ and the holder 30 to be assembled more easily . fig2 shows another embodiment of an inner sleeve 40 ′″ which can be used , e . g ., in the embodiment of fig1 - 21 in place of the sleeve 40 . the sleeve 40 ′″ is similar to sleeve 40 except that the connecting portions cp ″ in the instant embodiment is formed by a joint formed by circular projection bp ′ and a socket recess sr ′ which forms a pivot bearing for the projection bp ′. the circular projection bp ′ and the socket recess sr ′ are connected to each other via a small connecting band which forms a living hinge lh . the advantage of this joint cp ″ system is that it allows arc - shaped members 40 ′″ a and 40 ′″ b forming the sleeve 40 ′″ to pivot relative to each other more easily , i . e ., when the cap 50 is moved to the closed position and the tapered surfaces tpe engage the tapered surfaces tde . as was the case in the embodiment of fig1 , the sleeve 40 ′″ is a one - piece member with arc - shaped members 40 ′″ a and 40 ′″ b connected to each other via the two living hinges lh . fig2 - 29 show another non - limiting embodiment of a blood collection device 100 according to the invention . the device 100 includes a generally cylindrical outer sleeve or outer body member 200 which includes a proximal end 200 a configured to allow an external needle n of a double - ended needle member or holder 300 to pass therethrough , and a distal end 200 b which can be closed off by a cap 500 . an inner flange if is arranged at the proximal end 200 a . the needle holder 300 has an outer circumferential surface ocs ( see fig2 ) which frictionally engages with an inner circumferential surface ics ( see fig2 ) of a proximal end of an inner sleeve 400 . the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 100 also includes a spring 600 which functions to move the needle holder 300 distally when the outer circumferential surface ocs of the needle holder 300 is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 400 . once a user moves the cap 500 to the closed position , the sleeve 400 is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 300 no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 400 . the spring 600 is then free to move the needle holder 300 within the sleeve 400 in a distal direction which ensures that the needle holder 300 is fully and safely arranged within the device 100 . the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 400 from the needle holder 300 functions as follows . the sleeve 400 is prevented from moving axially backwards within the body 200 by a circumferential tapered shoulder ts engaging an inner tapered shoulder its of the body 200 , but is biased towards this direction by the spring 600 which , in fig2 , is substantially fully compressed . the sleeve 400 has a plurality of proximal slots ps which divide the proximal end of the sleeve 400 into a plurality of spring fingers each having a portion of the surface ics . a ring - shaped retaining sleeve rss is movably mounted to the sleeve 400 and is movable between the locked position shown in fig2 and 26 , and an unlocked position characterized by movement of the ring rss in the distal direction or movement of the sleeve 400 in the proximal direction while the sleeve rss remains static ( similar to that shown in fig3 . when the sleeve 400 is moved in the proximal direction by the closing of the cap 500 , the sleeve rss contacts an annular surface the tapered shoulder its preventing the sleeve rss from further movement in the proximal direction . the sleeve 400 , however , continues to move in the proximal direction . when a point is reach where the sleeve rss is moved sufficiently to the unlocked position , the spring fingers formed by the proximal slots ps are free to expand radially thereby releasing the engagement between the surface ics of the sleeve 400 and the surface ocs of the holder 300 . as a result , the proximal slots ps widen . this movement of the sleeve 400 and disengagement of the surfaces ics and ocs is caused to occur automatically when the user moves the cap 500 to the closed position , and more specifically , when an annular surface or proximal end of cap 500 contacts an annular surface or distal end of the sleeve 400 and forces the sleeve 400 to move axially in the proximal direction . thus , when the user moves the cap 500 to the closed position ( not shown ), axial movement of the sleeve 400 and movement of the sleeve rss relative to the sleeve 400 automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 300 and the sleeve 400 , the disengagement of these surfaces leaves the holder 300 free to move axially distally . furthermore , because the spring 600 maintains a biasing force against the holder 300 , when this engagement is released , the spring 600 will automatically expand axially and force the holder 300 to move distally within the sleeve 400 . this , in turn , results in the needle n being retracted into the sleeve 400 and positions it safely within the body 200 . the device 100 is then rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 100 . with reference to fig2 - 29 , it can be seen that the sleeve 400 , the retaining sleeve rss , and the needle holder 300 constitute a sub - assembly . the proximal end of the sleeve 400 forms a plurality of arc - shaped sections or fingers divided by equally spaced slots ps . as such , these fingers are free to deflect outwardly or to slightly elastically deformed outwardly . however , the sleeve rss functions to prevent this movement and ensures that the fingers are pressed tightly against the holder 300 , and more specifically , that the surfaces osc and ics remain in engagement until the sleeve rss is moved to a position which allows the fingers to deflect outwardly . in order to assemble the sub - assembly shown in fig2 , one need only slide the holder 300 into the proximal end of the sleeve 400 and thereafter slide the sleeve rss onto the distal end of the sleeve 400 and up to and over stop projections arranged on the sleeve 400 as is shown in fig2 . the holder 300 is then prevented from moving axially relative to the sleeve 400 by virtue of engagement between the tapered circumferential projection tcp and the corresponding shaped recess in the surface ics . fig3 shows another non - limiting embodiment of a blood collection device 100 ′ according to the invention . the device 100 ′ includes a generally cylindrical outer sleeve or outer body member 200 ′ which includes a proximal end 200 ′ a configured to allow an external needle n of a double - ended needle member or holder 300 to pass therethrough , and a distal end which can be closed off by a cap ( not shown ). an inner flange if is arranged at the proximal end 200 ′ a . the needle holder 300 has an outer circumferential surface ocs which frictionally engages with an inner circumferential surface ics of a proximal end of an inner sleeve 400 ′. the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 100 ′ also includes a spring 600 which functions to move the needle holder 300 distally when the outer circumferential surface ocs of the needle holder 300 is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 400 ′. once a user moves the cap 500 to the closed position , the sleeve 400 ′ is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 300 no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 400 ′. the spring 600 is then free to move the needle holder 300 within the sleeve 400 ′ in a distal direction which ensures that the needle holder 300 is fully and safely arranged within the device 100 . the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 400 ′ from the needle holder 300 functions as follows . the sleeve 400 ′ is prevented from moving axially backwards within the body 200 ′ by a circumferential tapered shoulder ( similar to shoulder ts ′ of fig3 ), but is biased towards this direction by the spring 600 which , in fig3 , is almost fully compressed . the sleeve 400 ′ has a plurality of proximal slots ps which divide the proximal end of the sleeve 400 ′ into a plurality of spring fingers each having a portion of the surface ics . a ring - shaped retaining sleeve rss is movably mounted to the sleeve 400 ′ and is movable between a locked position and the unlocked position shown in fig3 which occurs upon movement of the ring rss in the distal direction or more accurately movement of the sleeve 400 ′ in the proximal direction while the sleeve rss remains static , i . e ., prevented from proximal movement by the shoulder its . when the sleeve 400 ′ is moved in the proximal direction by the closing of the cap 500 , the sleeve rss contacts an annular surface the tapered shoulder its preventing the sleeve rss from further movement in the proximal direction . the sleeve 400 ′, however , continues to move in the proximal direction . when a point is reach where the sleeve rss is moved sufficiently to the unlocked position ( as is shown in fig3 ), the spring fingers formed by the proximal slots ps are free to expand radially thereby releasing the engagement between the surface ics of the sleeve 400 ′ and the surface ocs of the holder 300 . as a result , the proximal slots ps widen . this movement of the sleeve 400 ′ and disengagement of the surfaces ics and ocs is caused to occur automatically when the user moves the cap 500 to the closed position , and more specifically , when an annular surface or proximal end of cap 500 contacts an annular surface or distal end of the sleeve 400 ′ and forces the sleeve 400 ′ to move axially in the proximal direction . thus , when the user moves the cap 500 to the closed position ( not shown ), axial movement of the sleeve 400 ′ and movement of the sleeve rss relative to the sleeve 400 ′ automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 300 and the sleeve 400 ′, the disengagement of these surfaces leaves the holder 300 free to move axially distally . furthermore , because the spring 600 maintains a biasing force against the holder 300 , when this engagement is released , the spring 600 will automatically expand axially and force the holder 300 to move distally within the sleeve 400 ′. this , in turn , results in the needle n being retracted into the sleeve 400 ′ and positions it safely within the body 200 ′. the device 100 ′ is then rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 100 ′. as was the case with the previous embodiment , the sleeve 400 ′, the retaining sleeve rss , and the needle holder 300 constitute a sub - assembly . the proximal end of the sleeve 400 ′ forms a plurality of arc - shaped sections or fingers divided by equally spaced slots ps . as such , these fingers are free to deflect outwardly or to slightly elastically deformed outwardly . however , the sleeve rss functions to prevent this movement and ensures that the fingers are pressed tightly against the holder 300 , and more specifically , that the surfaces osc and ics remain in engagement until the sleeve rss is moved to a position which allows the fingers to deflect outwardly . in order to assemble this sub - assembly , one need only slide the holder 300 into the proximal end of the sleeve 400 ′ and thereafter slide the sleeve rss onto the distal end of the sleeve 400 ′ and up to and over stop projections arranged on the sleeve 400 ′. the holder 300 is then prevented from moving axially relative to the sleeve 400 ′ by virtue of engagement between the tapered circumferential projection tcp and the corresponding shaped recess or groove g in the surface ics . fig3 - 33 show another non - limiting embodiment of a blood collection device 100 ″ according to the invention . the device 100 ″ includes a generally cylindrical outer sleeve or outer body member 200 ″ which includes a proximal end 200 ″ a configured to allow an external needle n of a double - ended needle member or holder 30 to pass therethrough , and a distal end which can be closed off by a cap 500 ′. an inner flange if is arranged at the proximal end 200 ″ a . the needle holder 30 has an outer circumferential surface ocs which frictionally engages with an inner circumferential surface ics of a proximal end of an inner sleeve 400 ″. the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 100 ″ also includes a spring 600 which functions to move the needle holder 30 distally when the outer circumferential surface ocs of the needle holder 30 is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 400 ″. once a user moves the cap 500 ′ to the closed position , the sleeve 400 ″ is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 30 no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 400 ″. the spring 600 is then free to move the needle holder 30 within the sleeve 400 ″ in a distal direction which ensures that the needle holder 30 is fully and safely arranged within the device 100 ″. the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 400 ″ from the needle holder 30 functions as follows . the sleeve 400 ″ is prevented from moving axially backwards within the body 200 ″ by a circumferential tapered shoulder ts ′, but is biased towards this direction by the spring 600 which , in fig3 , is almost fully compressed . the sleeve 400 ″ has a plurality of proximal slots ps which divide the proximal end of the sleeve 400 ″ into a plurality of spring fingers each having a portion of the surface ics . the proximal end of the spring fingers or the sleeve 400 ″ includes a circumferential tapered portion tp 1 which is configured to engage with an annular or circumferential tapered portion tp 2 of the body 200 ″ when the sleeve 400 ″ is moved in the proximal direction by the cap 500 ′. furthermore , when the sleeve 400 ″ is moved in the proximal direction by the closing of the cap 500 ′, the tapered surfaces tp 1 of the spring fingers of the sleeve 400 ″ contacts the tapered surface tp 2 and causes the spring fingers formed by the proximal slots ps to expand radially thereby releasing the engagement between the surface ics of the sleeve 400 ″ and the surface ocs of the holder 30 . as a result , the proximal slots ps widen . this movement of the sleeve 400 ″ and disengagement of the surfaces ics and ocs is caused to occur automatically when the user moves the cap 500 ′ to the closed position , and more specifically , when an annular surface or proximal end of cap 500 ′ contacts an annular surface or distal end of the sleeve 400 ″ and forces the sleeve 400 ″ to move axially in the proximal direction . thus , when the user moves the cap 500 ′ to the closed position ( not shown ), axial movement of the sleeve 400 ″ automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 30 and the sleeve 400 ″, the disengagement of these surfaces leaves the holder 30 free to move axially distally . furthermore , because the spring 600 maintains a biasing force against the holder 30 , when this engagement is released , the spring 600 will automatically expand axially and force the holder 30 to move distally within the sleeve 400 ″. this , in turn , results in the needle n being retracted into the sleeve 400 ″ and positions it safely within the body 200 ″. the device 100 ″ is then rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 100 ″. as was the case with some previous embodiments , the sleeve 400 ″ and the needle holder 30 constitute a sub - assembly . the proximal end of the sleeve 400 ″ forms a plurality of arc - shaped sections or fingers divided by equally spaced slots ps . the slots ps can be a few as two oppositely arranged slots or as many as , e . g ., 20 or more , with any whole number between 2 and 20 being utilized . as such , these fingers are free to deflect outwardly or to slightly elastically deformed outwardly . however , the spring fingers include breakable and / or stretchable connections bec ( see fig3 ) which are designed to break or stretch when the spring fingers are caused to radially expand beyond a certain point , as occurs when the surface tp 1 engages with the surface tp 2 . these integrally formed members bec also ensure that the fingers are pressed tightly against the holder 30 , and more specifically , that the surfaces osc and ics remain in engagement until the surface tp 1 engages significantly with the surface tp 2 which allows the fingers to deflect outwardly . in order to assemble this sub - assembly , one need only slide the holder 30 into the proximal end of the sleeve 400 ″. the holder 30 is then prevented from moving axially relative to the sleeve 400 ″ by virtue of engagement between the projections cpp ( see fig1 ) and the corresponding shaped recess ( s ) or groove ( s ) in the surface ics . fig3 show another non - limiting embodiment of a blood collection device 100 ′″ according to the invention . the device 100 ′″ includes all of the features of the embodiment of fig3 - 33 , except that the sleeve 400 ′″ a stop slot opening sso which receives therein a projection p of the type used in the embodiment shown in fig1 , instead of the shoulder ts ′. the device 100 ′″ otherwise functions in the same way as that of fig3 - 33 . fig3 - 36 show another non - limiting embodiment of a blood collection device 100 iv according to the invention . the device 100 iv includes all of the features of the embodiment of fig3 - 33 or the embodiment of fig3 , except that the surface ics utilizes a tapered groove g and the surface ocs utilizes either a continuous tapered circumferential projection which generally corresponds in shape to the groove g or a plurality of tapered projections having the configuration shown . the device 100 iv otherwise functions in the same way as that of fig3 - 33 . fig3 and 38 show another non - limiting embodiment of a blood collection device 100 v according to the invention . the device 100 v includes a generally cylindrical outer sleeve or outer body member 200 iv which includes a proximal end 200 v a configured to allow an external needle n of a double - ended needle member or holder 30 to pass therethrough , and a distal end which can be closed off by a cap ( not shown ). an inner flange if is arranged at the proximal end 200 iv a . the needle holder 30 has an outer circumferential surface ocs which frictionally engages with an inner circumferential surface ics of a proximal end of an inner sleeve 400 iv . the sleeve 400 v can have a configuration similar to that of fig1 except that the taper tde is not utilized , and instead the distal end is configured to be similar to the distal end shown in the sleeve 400 ″ of fig3 . the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 100 v also includes a spring 600 which functions to move the needle holder 30 distally when the outer circumferential surface ocs of the needle holder 30 is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 400 v . once a user moves the cap to the closed position , the sleeve 400 v is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 30 no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 400 v . the spring 600 is then free to move the needle holder 30 within the sleeve 400 v in a distal direction which ensures that the needle holder 30 is fully and safely arranged within the device 100 v . the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 400 v from the needle holder 30 functions as follows . the sleeve 400 v is prevented from moving axially backwards within the body 200 iv by either a circumferential tapered shoulder ( similar to shoulder ts ′ of fig3 ) or by projections ( similar to projections p of fig1 ), and is biased towards this distal direction by the spring 600 which , in fig3 , is almost fully compressed . the sleeve 400 v has a plurality of proximal slots ps which divide the proximal end of the sleeve 400 v into a plurality of spring fingers each having a portion of the surface ics . the body 200 iv includes two oppositely arranged tapered projections oatp arranged therein which are each configured to engage ( i . e ., wedge open ) with one of the proximal slots ps of the sleeve 400 v when the sleeve 400 v is moved in the proximal direction by the cap . furthermore , when the sleeve 400 v is moved in the proximal direction by the closing of the cap , the tapered surfaces of the projections oatp are contacted the side surfaces of the spring fingers defined by the slots ps and causes the spring fingers formed by the proximal slots ps to expand radially thereby releasing the engagement between the surface ics of the sleeve 400 v and the surface ocs of the holder 30 . as a result , the proximal slots ps widen . this movement of the sleeve 400 v and disengagement of the surfaces ics and ocs is caused to occur automatically when the user moves the cap to the closed position , and more specifically , when an annular surface or proximal end of cap contacts an annular surface or distal end of the sleeve 400 v and forces the sleeve 400 v to move axially in the proximal direction . thus , when the user moves the cap to the closed position ( not shown ), axial movement of the sleeve 400 v automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 30 and the sleeve 400 v , the disengagement of these surfaces leaves the holder 30 free to move axially distally . furthermore , because the spring 600 maintains a biasing force against the holder 30 , when this engagement is released , the spring 600 will automatically expand axially and force the holder 30 to move distally within the sleeve 400 v . this , in turn , results in the needle n being retracted into the sleeve 400 v ( similar to the way shown in fig3 ) and positions it safely within the body 200 iv . the device 100 v is then rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 100 v . as was the case with some previous embodiments , the sleeve 400 v and the needle holder 30 constitute a sub - assembly . the proximal end of the sleeve 400 v forms a plurality of arc - shaped sections or fingers divided by equally spaced slots ps . the slots ps can be a few as two oppositely arranged slots or as many as , e . g ., 20 or more , with any whole number between 2 and 20 being utilized . as such , these fingers are free to deflect outwardly or to slightly elastically deformed outwardly . furthermore , the spring fingers can include breakable and / or stretchable connections ( similar to connections bec shown in fig3 ) which are designed to break or stretch when the spring fingers are caused to radially expand beyond a certain point , as occurs when the slots ps engages with the tapered surfaces of the projections oatp . these integrally formed members bec also ensure that the fingers are pressed tightly against the holder 30 , and more specifically , that the surfaces osc and ics remain in engagement until the slots ps engage with the tapered surfaces of the projections oatp which allows the fingers to deflect outwardly . in order to assemble this sub - assembly , one need only slide the holder 30 into the proximal end of the sleeve 400 v . the holder 30 is then prevented from moving axially relative to the sleeve 400 v by virtue of engagement between the projections cpp ( see fig1 ) and the corresponding shaped recess ( s ) or groove ( s ) in the surface ics . fig3 shows another non - limiting embodiment of a blood collection device 100 vi according to the invention . the device 100 vi includes all of the features of the embodiment of fig2 - 38 , except that instead of two proximal slots ps , the sleeve 400 vi utilizes four proximal slots ps , and the body 200 v utilizes four equally angularly spaced projections oatp instead of just two oppositely arranged projections . the device 100 vi otherwise functions in the same way as that of fig3 - 38 . fig4 and 41 show another non - limiting embodiment of a blood collection device 100 vii according to the invention . the device 100 vii includes a generally cylindrical outer sleeve or outer body member 200 v which includes a proximal end 200 v a configured to allow an external needle n of a double - ended needle member or holder 30 to pass therethrough , and a distal end which can be closed off by a cap 500 ″. an inner flange if is arranged at the proximal end 200 v a . the needle holder 30 has an outer circumferential surface ocs which frictionally engages with an inner circumferential surface ics of a proximal end of an inner sleeve 400 vii . the sleeve 400 vii can have a configuration similar to that of fig1 except that the taper tde is not utilized , and the proximal slots ps are made wider than the distal slots ds . the surfaces ics and ocs have generally corresponding shapes and need not be straight or cylindrical , i . e ., they can also be , e . g ., tapered or have an other non - straight shapes . the device 100 vii also includes a spring 600 which functions to move the needle holder 30 distally when the outer circumferential surface ocs of the needle holder 30 is released from frictional engagement with the inner circumferential surface ics of the proximal end of the inner sleeve 400 vii . once a user moves the cap 500 ″ to the closed position , the sleeve 400 vii is caused to move axially in the proximal direction which , in turn , causes outer circumferential surface ocs of the needle holder 30 no longer frictionally engage with the inner circumferential surface ics of the proximal end of the inner sleeve 400 vii . the spring 600 is then free to move the needle holder 30 within the sleeve 400 vii in a distal direction which ensures that the needle holder 30 is fully and safely arranged within the device 100 vii . the device can then be safely handled and discarded . the disengagement of the proximal end of the sleeve 400 vii from the needle holder 30 functions as follows . the sleeve 400 vii is prevented from moving axially backwards within the body 200 v by the oppositely arranged projections p 1 , and is biased towards this distal direction by the spring 600 which , in fig4 , is almost fully compressed . the sleeve 400 vii has a plurality of proximal slots ps which divide the proximal end of the sleeve 400 vii into a plurality of spring fingers each having a portion of the surface ics . the body 200 v includes two oppositely arranged circular projections p 2 arranged therein which are each configured to engage ( i . e ., wedge open ) with one of the proximal slots ps of the sleeve 400 vii when the sleeve 400 vii is moved in the proximal direction by the cap 500 ″. furthermore , when the sleeve 400 vii is moved in the proximal direction by the closing of the cap 500 ″, the tapered surfaces of the proximal slot ps are contacted the circular surface of the projection p 2 and this causes the spring fingers formed by the proximal slots ps to expand radially thereby releasing the engagement between the surface ics of the sleeve 400 vii and the surface ocs of the holder 30 . as a result , the proximal slots ps widen . this movement of the sleeve 400 vii and disengagement of the surfaces ics and ocs is caused to occur automatically when the user moves the cap 500 ″ to the closed position , and more specifically , when an annular surface or proximal end of cap 500 ″ contacts an annular surface or distal end of the sleeve 400 vii and forces the sleeve 400 vii to move axially in the proximal direction . thus , when the user moves the cap 500 ″ to the closed position ( not shown ), axial movement of the sleeve 400 vii automatically causes the surface ics to separate from the surface ocs . since the frictional engagement between the surface ics and the surface ocs constitutes the only engagement or connection between the holder 30 and the sleeve 400 vii , the disengagement of these surfaces leaves the holder 30 free to move axially distally . furthermore , because the spring 600 maintains a biasing force against the holder 30 , when this engagement is released , the spring 600 will automatically expand axially and force the holder 30 to move distally within the sleeve 400 vii . this , in turn , results in the needle n being retracted into the sleeve 400 vii and positions it safely within the body 200 v . the device 100 vii is then rendered unusable , i . e ., cannot be reused , and can be safely handled and disposed of without fear of the needle causing injury to persons who handle the used device 100 vii . as was the case with some previous embodiments , the sleeve 400 vii and the needle holder 30 constitute a sub - assembly . the proximal end of the sleeve 400 vii forms a plurality of arc - shaped sections or fingers divided by equally spaced slots ps . the slots ps can be a few as two oppositely arranged slots or as many as , e . g ., 20 or more , with any whole number between 2 and 20 being utilized . as such , these fingers are free to deflect outwardly or to slightly elastically deformed outwardly . furthermore , the spring fingers can include breakable and / or stretchable connections ( similar to connections bec shown in fig3 ) which are designed to break or stretch when the spring fingers are caused to radially expand beyond a certain point , as occurs when the slots ps engages with the circular projections p 2 . these integrally formed members bec also ensure that the fingers are pressed tightly against the holder 30 , and more specifically , that the surfaces osc and ics remain in engagement until the tapered surfaces of the slots ps engage with the circular projections p 2 which allows the fingers to deflect outwardly . in order to assemble this sub - assembly , one need only slide the holder 30 into the proximal end of the sleeve 400 vii . the holder 30 is then prevented from moving axially relative to the sleeve 400 vii by virtue of engagement between the projections cpp ( see fig1 ) and the corresponding shaped recess ( s ) or groove ( s ) in the surface ics . fig4 shows another non - limiting embodiment of a blood collection device 100 viii according to the invention . the device 100 viii includes all of the features of the embodiment of fig4 - 41 , except that the projections p 1 and the distal slots ds are not utilized , and instead tapered stop shoulder projections ts ″ are utilized to prevent distal movement of the sleeve 400 viii . the device 100 viii otherwise functions in the same way as that of fig4 - 41 . the devices described above can also utilize one or more features disclosed in the prior art documents expressly incorporated by reference herein . furthermore , one or more of the various parts of the device can preferably be made as one - piece structures by e . g ., injection molding , when doing so reduces costs of manufacture . non - limiting materials for most of the parts include synthetic resins such as those approved for syringes , blood collection devices , or other medical devices . furthermore , the invention also contemplates that any or all disclosed features of one embodiment may be used on other disclosed embodiments , to the extent such modifications function for their intended purpose . it is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention . while the present invention has been described with reference to an exemplary embodiment , it is understood that the words which have been used herein are words of description and illustration , rather than words of limitation . changes may be made , within the purview of the appended claims , as presently stated and as amended , without departing from the scope and spirit of the present invention in its aspects . although the present invention has been described herein with reference to particular means , materials and embodiments , the present invention is not intended to be limited to the particulars disclosed herein ; rather , the present invention extends to all functionally equivalent structures , methods and uses , such as are within the scope of the appended claims .
retractable medical device including a body having an open back end and a front end . a movable member is arranged within the body . the movable member has a back end and a front end . a needle holding member is arranged in an area of the front end of the movable member . a spring is structured and arranged to move the needle holding member to a retracted position within the movable member when the movable member experiences at least one of : the front end of the movable member is caused to expand generally radially ; the back end of the movable member is caused to contract generally radially ; the front end of the movable member is caused to expand generally radially when the back end of the movable member is caused to contract generally radially ; and axial movement caused by a cap closing off the back end of the body which engages a tapered surface of the back end of the movable member . this abstract is not intended to define the invention disclosed in the specification , nor intended to limit the scope of the invention in any way .