I was looking for a way to keep my house key from scratching stuff in my pocket. I was inspired by kwfredeen's cover, but wanted something that “stayed” on, was easy to remove, and easy to tell which side went up.
This cover features a textured side to get it right side up, and a spring loaded detent for retainment. If the first bump on the key is small, this may not work for you.
Note I left both the model and the cut-away model in there, for testing fit, and a second object makes it less likely to overheat.
The author remixed this model.