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