This complete upper includes our ATLAS R-ONE Handguard. The R-ONE handguards are designed with size and weight in mind, while still providing plenty of real-estate to accommodate any attachment needs the end user may have. Our proprietary ATLAS attachment system is a durable and dependable mounting platform, maintaining a slim profile while still providing the strength and stability customers have grown to love from Aero Precision handguards. Specifications for Aero Precision M4E1 Threaded 10.5in 5.56 Complete Upper Receiver with Flash Hider: Manufacturer: Aero Precision Cartridge: 5.56x45mm NATO Barrel Length: 10.5 in Barrel Profile: Government Gas System Length: Carbine Length Barrel Twist Rate: 1-7 Muzzle Device: A2 Flash Hider Gun Model: AR-15 Condition: New Gas Block Journal Size-Diameter: .750 in Handguard Length: 9 in Magazine Included: No Country of Origin: USA Features of Aero Precision M4E1 Threaded 10.5in 5.56 Complete Upper Receiver with Flash Hider Enhanced forging that gives the upper receiver a "billet look". Picatinny profile that blends seamlessly with our Enhanced Series Handguards. .250 takedown pin holes. Laser engraved T-marks. Includes port door and forward assist installed. Full top picatinny rail for optional attachments. Quick disconnect sling socket at the 3, 6 and 9 o'clock positions. Compatible with low profile gas blocks. Compatible with mil-spec AR15 upper receivers and barrels. Package Contents: Aero Precision M4E1 Threaded 10.5in 5.56 Complete Upper Receiver with Flash Hider