as appears from the drawings , an embodiment of a fastening device 1 according to the invention consists of a hollow house 4 with a lid 5 , the cavity containing a washer 3 , a first spring 7 , a second spring 8 and a ball 9 . a peg 2 , which is put through a central hole 44 in the house and through a central aperture or hole 31 in the washer and possibly further on through a central hole 51 in the lid is secured from being moved apart by the washer 3 , seated on the ball 9 and the central aperture 31 of which is securing to the peg 2 by the force from the springs 7 and 8 . the fastening device 1 is also equipped with a releasing device 6 , bringing the washer against the force of springs 7 and 8 in order to release the peg 2 from engagement in the hole 31 of the washer 3 . in order to obtain a secure function of the device certain conditions must be fulfilled . the ball 9 should be in a position mainly diametrically opposed to the outer , first spring 7 , which secures the locking action of the washer . the inner , second spring 8 serves to keep the washer 3 in contact with the ball 9 as the peg is inserted so that no backlash will arise in the locking function caused by that the washer is moved from the ball towards the lid when the peg is inserted . in order to fulfil thin function the second spring 8 should be situated near the ball , preferrably between the ball and the hole for the peg , and its spring force should be substantially bigger than that of the first spring 7 . the springs 7 and 8 are coil springs kept in place by being countersunk in and / or fastened to the lid . the springs 7 and 8 may also be made of conical coil springs in order to reduce the height of the fastening device . alternatively , one or both springs may be made as plate springs with tongues springing out from a spring bottom which bears on the lid 5 . it is also possible to replace the springs 7 and 8 with one single coil spring with a suitable dimensioning and placement , for instance around the hole 31 . moreover , the washer 3 must be so designed , that its central hole 31 has a diameter slightly bigger than that of the peg 2 . with 8 mm diameter of the peg 2 and a thickness of 1 . 5 mm of the washer 3 it is suitable that the diameter of the hole is up to 0 . 1 mm bigger , preferrably 0 . 04 - 0 . 05 mm bigger than that of the peg 2 . it is the combination of a ball 9 , against which the washer easily can slide or roll , and the mainly diametrically contacting spring 7 , against which the washer also can slide with a low friction , that makes the washer lock securely also if the peg with the washer are turned in relation to the fastening device . this is , of course , possible to achieve otherwise than with the ball 9 . this can for instance be substituted by every other discrete contact point which can give the same quality with or without lubrication , such as a sliding surface , a roll or the like . the contact points of the springs towards the washer may be made of a ball , a bearing surface or another suitable design as well . it is also possible as an alternative within the scope of this invention , even though this gives a more complicated construction , to surround the washer , its contact point and the springs with a bearing in the house so they can rotate with the peg . the house 4 consists of a main part 41 with a cylindrical cavity or recess 42 , with a central hole 44 , also leading through a threaded part 43 arranged on the bottom side of the main part . the wall 45 of the main part extends in the shape of half a circle around one half of the recess 42 but forms around the other half a rectangular profile , through which a channel 48 for the releasing device 6 runs . the channel 48 is arranged with its center line at the bottom of the cylindrical recess 42 in such a way that all of the channel for one part is situated within the circumference of the recess 42 . around the upper part of the recess 42 an enlargement 46 is made so that the lid 5 can be mounted therein , preferrably with a snap action . at the bottom of the recess is also arranged a countersink 47 for the ball 9 . the releasing device 6 consists of a shaft 61 ground with at least one conical part 63 to a narrow part 62 of even thickness , normally situated opposite the middle of the washer 3 . one end of the shaft 61 is threaded and equipped with a nut 65 and a sleeve 66 and a coil spring 67 is arranged between the nut 65 and the main part 41 of the house . the shaft 61 is retained against action of the spring 67 by a screw 68 arranged at the end of the shaft with its head normally bearing upon the house 4 . the function of the releasing device 6 is such that its conical part 63 lifts the washer 3 when the shaft 61 is moved axially by pressing on the sleeve 66 , by which the central hole 31 of the washer releases its hold of the peg 2 . the end of the peg is equipped with a thread 21 in order to be attached to for instance a prosthesis sleeve , and the house 4 with its threaded part 43 can be attached to a prosthesis , or vice versa . the invention has now been described in detail with reference to a preferred embodiment . however , several modifications are possible within the scope of the invention , which shall only be restricted by the wording of the following claims . thus , when appropriate , the peg can be substituted by a long rod or a tube and the releasing device can be substituted by every other suitable mechanism influencing the washer from its inclined position towards a position perpendicular to the peg . of course , the design of the house and the lid can also be altered .
a fastening device for a prosthesis , the fastening device having a cylindrical channel and an inclined washer designed to accept insertion of a cylindrical inset , such as a tube , bar or peg , with minimal resistance and yet substantially prevent withdrawal of the cylindrical insert from the fastening device unless a release mechanism is operated to permit withdrawal . the device permits rotation of the cylindrical inset with respect to the fastening device while still securely fastening the cylindrical insert within the fastening device , so as to prevent unlocking of the device and separation of the cylindrical insert .