The FAB Defense Ultimag 10R Pentagon Magazine Kit is a unique, ergonomic accessory that will greatly enhance your firepower while complying with a 10 cartridge limitation. FAB Defense constructed these Gun Accessories from rugged high-grade polymer, and you can use these kits on M16, M4 or AR15 variants. This FAB Defense Ultimag 10R Pentagon Mag Kit features an external coupler that doesn't replace the magazine floor plate. Add incredible tactical utility to your rifle with this FAB Defense Ultimag 10R Pentagon Magazine Kit. FEATURES • Highly ergonomic design.