The M4E1 Threaded Upper Receiver features an angular machined design that helps it stand apart from standard mil-spec upper receivers. This upper receiver features the same enhanced body profile as Aero's M4E1 Enhanced Upper Receiver but is threaded to accept a standard AR-15 barrel nut. It is forged from 7075-T6 Aluminum, precision machined to work with all mil-spec AR-15 parts and includes the port door and forward assist pre-installed. The M4E1 Threaded Upper Receiver is designed to pair perfectly with Aero's new M4E1 Lower Receiver, giving you a billet looking receiver.