A couple of things to print dust covers for a PL-259 and a SO-239.
These things are threaded, which means the tolerances are comparatively tight for printed 3D printed parts. You might have to print one, see if its too tight or too loose, and tweak the diameter slightly.

Don't bother with the Thingiverse customizer for this thing's scad file. Download from openscad dot org instead.

Prusa

i3 MK2.5

No

No

0.15

0.4mm nozzle and 0.15 layer height are what I printed successfully.

A brim of 1mm around the SO239 cap helps keep it from coming loose during printing.