I've been considering toying with semi-permanent chastity using aluminum pop rivets (which really aren't so permanent), but I was never successful in shop class and don't know what size rivet I'd want for the job. Looking at rivet sizing online makes my head spin and I was wondering if someone could suggest a rivet size for my Jail Bird (which has a .75"/19mm padlock right now).
It sounds like a 1/8"x1/4" (3mmx6mm) rivet would do it. Most hardware stores will sell an assorted pack of rivets right next to the guns so you can test it.