Knob - 3/8" inch

Knob which accepts a 3/8" nut or bolt.

Original model has variables which would let you resize this (to some degree) to fit other sized bolts.
https://cad.onshape.com/documents/4239ab9baf7ac7283d3f54d4/w/73ca030cee3d54ea36d31362/e/f8eab7bd6335ddfc7d68f796

I printed the knobs at 0.2mm and the caps a 0.1mm. X and Y scaled 107% to account for shrinkage. Uniform scaling would probably work however.