I have 3 of these little clamps that came with a bundle of parts related to a Pultra lathe. The clamps appear professionally made and are about 1" long and 0.5" wide. They have a spring to open the jaw when the large knurled nut is undone. The small knurled screw acts to tighten the clamp just as a machinists (or toolmakers) parallel clamp does. I am not entirely convinced that they belong with the lathe and I'd like to find out for sure what they are for. The jaws only open about 1/8" before the small locking screw reaches it's useful limit but the main screw is much longer. My leading thought is that they are clamps for holding thin disks (clock wheels and similar) onto the small face plate and that the extra length on the main screw allows the large thumb nut to secure the clamp to a slot in the face plate - as in the second photo. Does anyone know for sure?