The M4E1 Lower Receiver delivers billet aesthetics in a forged package. It is machined from 7075-T6 aluminum and compatible with all mil-spec AR15 parts. It features an integrated trigger guard, upper tension screw, and an increased magwell flare to aid in quick and efficient magazine changes. Included is a nylon tipped tensioning set screw and threaded bolt catch pin. Rear takedown pin detent hole is threaded for a 4-40 set screw. Threaded Bolt Catch Roll Pin (Included).