container holders adapted to hold a plurality of different - sized containers are described in this section . with reference to the figures generally , container holders are described which are adapted to provide a clamping force that is sufficient to grip typical fast - food sandwich clamshell boxes having a range of different sizes but insufficient to damage or undesirably deform the boxes . according to one embodiment illustrated in fig1 - 8 , a container holder 10 incorporating a substantially constant - force flat spiral spring 12 is described . according to an alternative embodiment , an alternative spring mechanism incorporating a variable - force spring 12 ′ is also described in this section , with reference to fig9 . referring generally to fig1 - 8 , the structure of container holder 10 incorporating a substantially constant - force flat spiral spring 12 is described in the following paragraphs . container holder 10 includes a pair of generally opposed prongs 14 and 16 , where prong 14 is shown as a right prong that is slidingly connected to a back plate 18 , and prong 16 is shown as a left prong that is fixedly attached to back plate 18 . turning to fig4 , a u - shaped base portion 20 of right prong 14 is slidingly received between lower slide tabs 22 a , b and upper slide tabs 24 a , b of back plate 18 . a protruding portion of a stop member 25 , seen in fig1 , 4 and 5 , substantially prevents base portion 20 from sliding further in the direction indicated by arrows e when base portion 20 impinges stop member 25 , thus preventing base portion 20 from sliding off of back plate 18 . stop member 25 is illustrated as a rivet having a base portion at the front side of a rib 27 of back plate 18 , as seen in fig6 and 7 , and extending backwardly therethrough , as seen in fig1 , 4 and 5 . alternatively , stop member 25 could be welded to or formed in rib 27 , or otherwise attached to any suitable part of back plate 18 so as to substantially prevent base portion 20 from sliding off of back plate 18 . fig8 is a fragmentary illustration of the integral attachment of right prong 14 to sliding base 20 , whereby a thinner bent rod 26 is welded to a thicker bent rod 28 . bent rod 26 includes a longitudinal portion 30 , a shoulder detent 32 a , and a vertical spring post 34 . bent rod 28 includes a longitudinal portion 36 and a transverse u - shaped base portion 20 which , as shown fully in fig4 , fits slidingly between slide tabs 22 a , b and 24 a , b . the structure of left prong 16 is shown in fig6 . similarly to right prong 14 , left prong 16 includes a thinner bent rod 40 welded to a thicker bent rod 42 . bent rod 40 includes a longitudinal portion 44 and a shoulder detent 32 b . bent rod 42 includes a longitudinal portion 48 and a transverse l - shaped base portion 50 which is welded to beads 52 , 54 and 56 of back plate 18 . in this manner , left prong 16 is fixedly attached to back plate 18 . back plate 18 itself additionally includes a hanging lip portion 58 , adapted for hanging back plate 18 on a suitable fixed vertical structure ( not shown ), and a stepped foot portion 60 , adapted for propping back plate 18 away from the fixed vertical structure , so as to avoid impingement of the structure by flat spiral spring 12 and / or by right prong 14 . with reference to fig4 and 6 , flat spiral spring 12 includes a spiral - coiled portion 62 which winds around spring post 34 of right prong 14 , and an uncoiled , generally flat portion 64 which connects by a spring lip 66 to spring receiving slot 68 in back plate 18 . the function of container holder 10 will now be described , with reference to fig1 - 7 . in fig1 - 3 , container holder 10 is shown holding a stack of nested quick service restaurant clamshell sandwich boxes b . the generally elongate shape of prongs 14 and 16 makes them particularly well suited to be received in notches n typically found at the ends of hinges h of clamshell boxes b . additionally , the disposition of thinner bent rods 26 and 40 inward and downward relative to thicker bent rods 28 and 42 matches the taper of the upper side of notches n , as best shown in fig3 , thus improving the frictional contact between prongs 14 and 16 and notches n by comparison to single - rod prongs . this frictional contact is beneficial , as it restrains or prevents accidental sliding of boxes b toward the ends of prongs 14 and 16 , as well as helping to retain the remainder of boxes b in place when a selected box b or plurality of boxes b are intentionally removed from container holder 10 . likewise , the inward curvature of shoulder detents 32 a , b is adapted so that they partially obstruct but do not wholly prevent the removal of boxes b , so that intentionally applying a sufficient force will remove boxes b that one desires to remove , but not boxes b that one desires to leave , including lower boxes b that “ cling ” to upper boxes b in which they are nested , for example . boxes b are held between prongs 14 and 16 by a clamping force represented by arrows f in fig1 - 3 . in the embodiment illustrated in fig1 - 8 , clamping force f is provided by substantially constant - force flat spiral spring 12 . in particular , spring 12 produces a force tending to wind up coiled portion 62 toward generally flat portion 64 , thereby pulling spring post 34 inwardly towards spring receiving slot 68 . in the fully retracted configuration of container holder 10 illustrated in fig4 and 7 , the base of right prong 14 is braced against the right edge of back plate 18 , as best seen in fig7 . in this configuration , there is no net clamping force between prongs 14 and 16 , and prong 14 is only free to move away from prong 16 to extend the width of the gap between prongs 14 and 16 in the direction indicated by arrows e . the fully retracted , minimum width of the gap between prongs 14 and 16 is denoted in fig4 and 7 as g r . on the other hand , in the extended configuration of container holder 10 illustrated in fig5 and 6 , right prong 14 is pulled away from the edge of back plate 18 and is free to retract in the direction indicated by arrows r as well as to extend further from prong 16 in the direction indicated by arrows e . in the extended configuration , the force of spring 12 results in a clamping force f tending to move prongs 14 and 16 back together towards the retracted configuration . because spring 12 is a substantially constant - force spring , clamping force f remains substantially the same over a range of extended gap widths g e , one example of which is shown in fig5 . thus , by appropriately selecting and configuring the elements of container holder 10 , and particularly the spring force provided by spring 12 , prongs 14 and 16 can be made to grip different boxes having a range of sizes firmly enough to retain the boxes , but not so firmly as to damage or undesirably deform the boxes . it should be noted that the maximum permitted gap width g e will be determined by the configuration of stop member 25 , as by preventing further extension movement of base member 20 , stop member 25 also prevents further extension movement of prong 14 away from prong 16 when base member 20 impinges stop member 25 . thus , stop member 25 should be configured to impinge base member 20 only when extended gap width g e is slightly larger than the width of the clamped portion of the largest box desired to be clamped . typically , clamping forces of at least about 0 . 1 lb are satisfactory to grip a typical quick service restaurant clamshell sandwich box b , and that forces no greater than about 1 . 5 lbs will not damage or undesirably deform a typical clamshell sandwich box b . the inventors have also noted that a container holder 10 with prongs 14 and 16 that may be adjusted to a range of gap widths of from about 2 . 5 inches to about 6 . 0 inches will accommodate a substantial variety of typical fast - food clamshell sandwich boxes b . thus , container holder 10 typically provides a clamping force f between prongs 14 and 16 that remains within the range of from about 0 . 1 pound to about 1 . 5 pounds over a range of gap widths between prongs 14 and 16 of from about 2 . 5 inches to about 6 . 0 inches . however , it should be noted that , although the illustrated container holder 10 is shown as used for holding boxes b , holders and methods of using holders for gripping any items of varying size firmly enough to hold the items , without gripping them too firmly , are included in the present invention . to accommodate such other items , appropriate adjustments may be made to the useful range of gap widths and the optimal range of clamping forces , as well as to the shape of prongs 14 and 16 or other suitable gripping members , without departing from the essential scope and spirit of the invention . referring to fig9 , an alternative manner in which a movable prong 14 ′ may be mounted to a back plate 18 ′ within the scope of the invention is illustrated . in this embodiment , a variable - force spring 12 ′ is employed in place of substantially constant - force spring 12 . in the illustrated example , variable - force spring 12 ′ is a helical spring that is connected to movable prong 14 ′ at spring post 34 ′ and to back plate 18 ′ at spring post 70 by spring hooks 72 . a helical spring in tension typically provides a variable tensile force that increases as the spring is extended beyond its relaxed length . for example , the tensile force is often approximated as being directly proportional to the difference between the extended and relaxed lengths . however , container holders incorporating such springs are within the scope of the present invention , to the extent that they provide a preferred range of clamping forces over a useful range of gap widths between their gripping members . it should also be noted that , even when employing a variable - force spring , the effect of force variation can be minimized by “ preloading ” the spring to an initial tension that is much greater than the variation in tension due to spring extension resulting from normal use , so that the variation in tension is rendered relatively insignificant . thus , a preloaded variable - force spring could be advantageously employed in the present invention in place of a substantially constant - force spring . while the invention has been described with respect to certain preferred embodiments , as will be appreciated by those skilled in the art , it is to be understood that the invention is capable of numerous changes , modifications and rearrangements , and such changes , modifications and rearrangements are intended to be covered by the following claims .
a container holder adapted to hold a container between two spaced apart prongs is provided herein . the prongs clamp the container with a clamping force large enough to hold the container , but small enough to avoid damaging the container . the prongs may be spaced apart to fit different - sized containers , while the clamping force still meets these criteria . the clamping force may be provided by a substantially constant - force spring or a variable - force spring . in a method according to the present invention , a stack of nested containers is held in a container holder as described , for subsequent removal of a selected container from the stack .