Summary

This is a knob for M2 screw with 3.5mm head. I made it specifically for the replacement screw for a caliper.

FreeCAD file is attached. Probably you'll want to increase the inner diameter of the hole to 3.7-4.0mm if you want to glue the screw head to the knob as I found that the actual hole diameter in the printed part is 3mm instead of 3.5mm. I just heated the screw and melted its head into the knob and that worked out fine for me.