Pentax rear lens cap for K-mount lenses. Designed to fit more tightly than the Pentax caps, especially on 3rd party lenses. These caps are also about 20% shorter but wide enough to seal against the o-rings on weather resistant lenses.
Tolerances are very tight on this design so I'm not sure how well it will work with other printers. Support material may be needed in some cases, but I've been printing without using ABS and MadeSolid PET+. Without support, my printer usually leaves a single loose line of filament that needs to be removed to keep it from snagging on the lens bayonet.