Shortening screws on belt sander works well and if screw is held concentrically it is easy to put a chamfer on the screw. Needed to shorten a 2-56 screw today so this is my side tracked project.
Both the fixed and moveable jaw are thread 2-56 so it is only good for 2-56.
Below is some that will hold other sizes but don't hold by thread. They hold by pushing the head against a shoulder. Idea for these is by Frank Ford who posted on another site.