I recently got some Mamiya 645 lenses to play around with, unfortunately without enough rear lenscaps. Being 25 € on Ebay I had to print them myself. The design is a bit like the original ones but modified for easier printing (no text, flat bottom, rounded gripcuts).
Works like a charm in PETG and has a snug fit.
I also added the STEP-File so you have an easier time modifying the part for yourself.
The author marked this model as their own original creation.