This is a carrier case for keeping your mags organized, it fits into a 4.5x3.4 Inches Clear Rectangle Box available on amazon.
This is for the .25cal avenger, not sure if other avenger mags from other calibers will fit as I don't have any to test out.

Update
Here is version 2, I added scallops to aid in removing the magazines as well as text that marks the mags for the avenger