The M4E1 Threaded Upper Receiver features an angular machined design that helps it stand apart from standard mil-spec upper receivers. It is threaded to accept a standard AR-15 barrel nut and forged from 7075-T6 aluminum and precision machined to work with all mil-spec AR-15 parts. The M4E1 features a picatinny profile M4 feed-ramps and .250 take-down pin holes. NOTE: Requires dust cover forward assist charging handle barrel handguard gas block muzzle device gas tube and BCG (Bolt Carrier Group) to complete.