This is a minimal effort work. This is just to make the finishing look nicer when you don't have the cable glands of the right colour in your stock.

Printing:

Printed with fuzzy skin but only outiside.

Material: PETG (because of outdoor use)

Adhesion: [no supports + raft] or [supports + skirt]

Original: https://www.tinkercad.com/things/2QfKhGE7vxN-cable-gland-cover-m16 

(adjust by yourself depending on the cable diameter)