When you are thinking about building a new AR-15 rifle or completing that lower you have had sitting around this CMMG AR-15 Carbine Receiver Extension Kit 6-position Mil-Spec is the perfect one. This kit contains an AR-15 carbine receiver extension, end plate, carbine buffer and spring.Features :Designed to work with both standard 5.556mm NATO AR rifle buildsHigh quality anodized aluminum