These are custom thumbscrews made for the ncstar/vism ar15 vise block/buffer tube tool, sized just right to let you tighten down the lower by hand via the grip screw hole without it poking out too far and hitting your vise. The unthreaded version obviously needs to be threaded with a 1/4-28 die (they're like six bucks at the hardware store, quit whining), while the threaded version prints with threads ready to go (not recommended, ymmv depending on your printer). I strongly suggest printing this with 3+ walls and 100% infill. If you plan on using this a lot you should use a lathe to make one out of steel instead, dimensions are listed below in metric (deal with it).

6.35mm D x 18.5mm L threaded section
9mm D x 25mm L shaft section
18mm D x 10mm L knurled section

LBRY Tags: ar15; guncad; gunsmithing; tool