I found many 3d printed lens cap on Thingiverse but after printing a whole and using them for a while I noticed that they get weak over time and the caps can fall easily. So I like to design hybrid 3d printed parts to reduce printing times, but this time I added a small part that I found in my office.
A small binder clip Nº 1 (also called 19mm or 3/4") these kind of clips are made with two arms that are made with a springy metal and this will eliminate the problem that I had with other 3d printed caps. And as a plus you can customize the cap with a logo or text like I did.
You can find all the free STL files and the tutorial in the links provided.