My leatherworking clamp was salvaged from the skip of a closed down factory.
It is the type that require 3 hands - 1 to hold it open and 2 to adjust the leather.
This modification solved the problem. Turned up from brass, the screw holds the jaws open untill the work is in the right place.
IMGP2768.jpg

Nothing very complicated, a length of threaded rod, a nut inserted in one arm of the clamp & a plate to push against in the other. Both nut and push plate glued in place with epoxy.

Mark