Are you tired of carrying around tons of keys? Give this a try. It will hold up to 6 keys using an 8/32 - 3/4" machine screw. If you want to add more, get a longer screw. Want less? Just add some washers as spacers (so the screw doesn't hang out of the other side.
Do you also have a CNC machine? Because I made some out of wood, if you'd like to check those out too!