About this 3D model

Chances are, if you've got any sort of collection of 50+ year old 16mm C-mount lenses, you've got a few that don't have lens caps. The fronts are all different, I can't help you there. But the back of the lens (the screw-on part) is (hopefully) the same as this cap, otherwise it wouldn't be a C-mount lens. The simple design is simple. No threads included, just push it or twist it on.