When nut 1 is turned (tightened) about fixed axis x-x, vise jaws 2 clamp workpiece 3. As nut 1 is tightened further, wedges a expand slotted spring bushings b, locking the vise jaws with respect to their guide. Springs 4 return the jaws to their initial position when nut 1 is released.
$242$SL,GC$