3/8"-16 Threaded Knob

This a knob I printed a bunch of copies to use as hold downs on a workbench where I had a pattern of holes with 3/8" thread inserts.   This is a 2 piece design you insert the nuts (standard 3/8" nuts, 9/16 wrench size) and then glue the insert in.

Recommend printing with increased perimeters for strength, I used 5.  I also added solid infill on the end of the wings to help it spin better, but you could just do the whole thing solid as well.