This is the SLR Camera Lens Cap by simonx tweaked to print fully assembled.

The spring part was resized in one dimension only and 0.5mm of the springy part was sliced off so that it was at least 0.5mm away from the cap portion.

The overhang of the cap part that traps the springy part was cut away so that it had at least the same 0.5mm of empty space. The two parts have no supports between them when sliced by Cura.

This was printed as a test on the lulzbot mini in ABS with a 0.25mm layer height. After supports were removed from the bottom, just a little persuasion with a screw clamp was required to get it moving. After it started working, repeatedly squeezing it for a few minutes made it operate smoothly. Sadly, this is the wrong size for any of my lenses. I was expecting (since the original said 51mm) to be able to enlarge by 1.31x and print for my lens that takes a 67mm lens cap (the math said 66.05mm and the actual print turned out to be 66.66mm), but I forgot to actually measure the lens, and it turned out the right size for a 67mm lens cap is 65.80mm. I re-made the lens cap model from scratch in Autodesk 123D Design at the right size for 67mm and uploaded it as 67mm-lens-cap-assembled.stl to eliminate an issue with too few polygon edges making up the circles.

This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/f7J2h4DQmsX

The 67mm version was made in autodesk 123d design:
http://www.123dapp.com/123D_Design/SLR-Camera-Lens-Cap-Single-Print-Experiment/4934390