From time to time, this comes up as a subject on the chat forums, and as we have been working on R&D the last while, I will post a method here.
To make a split nut screw, one can turn the head of the screw and the shaft while leaving a heavier shoulder diameter under the head. Drill a hole in a piece of tool steel, and use a small file to square up the top section to the desired length. Harden the steel, put the screw into the hole, and squeeze with the vise. Square shouldered screw.
From there, you must apply threads and make the nuts. It's not a walk in the park but, if you need to do it, it's a way. In fact, based on originals I have seen, they appear to have been "upset" in this same manner.
Regards,
Doug
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