M2 Armament Group AR-15 Threaded Stripped Upper Receiver Black. Engineered for demanding armorer standards professional builders and custom rifle fabricators this upper receiver delivers flawless mechanical alignment strict mil-spec internal dimensions and duty-ready durability. Specifications for M2 Armament Group AR-15 Threaded Stripped Upper Receiver: Manufacturer: M2 Armament Group Color: Black Fabric/Material: 7075-T6 Aluminum Caliber: 5.56x45mm NATO .300 AAC Blackout .223 Remington Gun Make: AR Platform Gun Model: AR-15 Package Contents: M2 Armament Group AR-15 Threaded Stripped Upper Receiver What firearm models does the manufacturer say M2 Armament Group AR-15 Threaded Stripped Upper Receiver is compatible with? The manufacturer suggests that M2 Armament Group AR-15 Threaded Stripped Upper Receiver is compatible with AR-15M2 Armament Group M2-UPPER-S: AR-15 Threaded Stripped Upper Receiver Black