Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4935582.

I designed this pouch to hold spare handgun magazines. It will fit one single-stack 9mm magazine. I tested with a Ruger EC9S magazine. It can be placed inside or outside of the waistband.

There is a little bit of extra space between the magazine and the case. If you want some friction between the two you could add some tape to the inside wall of the case.