The ATLAS R-ONE is the newest addition to the Aero Precision Handguard lineup. Machined from 6061-T6 Aluminum, the R-ONE line of handguards are designed with size and weight in mind, providing the perfect handguard for your lightweight build. 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.Features: 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 1.3" Inside diameter 1.5" Outside diameter Compatible with mil-spec AR15 upper receivers and barrels M4E1 Threaded Assembled Upper ReceiverThe M4E1 Threaded Assembled Upper Receiver features a new angular machined design that helps it stand apart from standard mil-spec upper receivers. This upper receiver features the same enhanced body profile as our M4E1 Enhanced Upper Receiver but is threaded to accept a standard AR15 barrel nut. It is forged from 7075-T6 Aluminum, precision machined to work with all mil-spec AR15 parts and includes the port door and forward assist pre-installed. Get the billet look without paying the billet price!M4E1 Threaded Upper Features: New enhanced forging that gives the upper receiver a "billet look" New picatinny profile that blends seamlessly with our Enhanced Series Handguards M4 Feedramps .250 takedown pin holes Laser engraved T-marks Includes port door and forward assist installedIncludes M4E1 Threaded Assembled Upper Receiver ATLAS R-ONE Handguard of choice Handguard Mounting Hardware