The CaldwellA(R) Mag Couplers are made out of high strength polymer to easily couple 2 Mil-Spec Style 10 round AR-15 magazines together and not add weight. The coupling of magazines brings your capacity up to 20 rounds for faster reloads when seconds matter. The coupler is a 2 piece design that is bolted together to be extremely rigid without permanently modifying your magazines. The couplers hold the 2 magazines end to end to maintain the overall shape of a 30 round magazine to fit in all of your existing gun cases, mag pouches, etc.