The Aero Precision M4E1-T 5.56 NATO is a complete upper receiver designed for AR-15 platform rifles. This upper prioritizes functionality and customization. The M4E1 Threaded Assembled Upper Receiver features a new enhanced design for a sleek look and easy integration with M-LOK handguards. It includes a port door and forward assist and is available in an OD green anodized finish.Features: M4E1 Threaded Assembled Upper Receiver Laser engraved T-marks10.3" ATLAS R-ONE M-LOK handguard 11.5" 5.56 NATO barrel with carbine-length gas system 1/7 twist rate, government profile barrel M4 feed ramps HP (High Pressure) and MPI (Magnetic Particle Inspected) tested barrel Standard A2 flash hider Made in America