When screw 3 is rotated, it imparts sliding motion to the rack 2 to which it is connected by a screw pair. This rotates ring gear 4 which meshes with three racks 2 so that the other two racks 2 are also moved the same amount. Racks 2 also have inclined rack teeth a that mesh with corresponding teeth on the base of chuck jaws 1. Thus, when screw 3 is rotated, jaws 1 are either advanced toward the centre to clamp the workpiece or they are retracted to release the workpiece.
$2288$LS,FD$