of the rail this movement of block 94 changes the angular position of frames 62 and 64 about the side rails 20 and 22 thereby forcing adjustment rail 74 longitudinally relative to block 94 so that the angular position of frames 46 and 48 changes with the change of angular position of frames 62 64 and the longitudinal position of block 94 in this way cross member pairs 44 60 are folded and extended according to the position of block 94 on rail 74 in order to change the width of the wheelchair referring next to fig7 adjustment block 94 is formed with two upper devices 110 and two lower devices 112 a device of each lateral pair located on opposite lateral sides of the center line of rail 74 a pin passing through those clevices hinges each attachment strut 92 98 on block 94 rail 74 supports block 94 so that the block can slide longitudinally to a position limited by the located of a collar 114 whose position on rail 74 is fixed by a set screw bolt or similar attachment 116 which engages rail 74 and fixes the position of collar 114 the upper surface of block 94 pivotally supports a latch 118 having a blocking surface 120 when the latch is in position shown in fig7 surface 120 engages the end face of collar 114 thereby releaseably fastening block 94 to rail 74 but not locking the block to the.