Toolmakers Machinist 3 inch Parallel Clamps - video

[Deez Workshop]

Can anyone explain how these work?
The end of the outside screw appears to go into a threaded hole instead of a blind hole, so it can only spread the clamping tips, not close them.

These are dual threaded on one side but to use them both screws will need adjusted in tandem to squeeze or clamp on your work piece, I do not have the end captive in one side like mose professional designed parallel clamps, (Starret etc.) These were my attempt at making a clamp and using Autocad for the first time.

Hope this helps

Deez Workshop.