Aero's M5E1 Upper Receiver is a one-piece design combining the handguard mounting platform with the upper itself. Aero has condensed the parts needed to mount a free-floated handguard to 8 screws. Since the handguard mounting surface and upper are of the same forging it a stronger system, but has additional lightening cuts to save weight and allow for more efficient cooling. Installation is easy simply insert your barrel assembly into the M5E1 upper, tighten it using the included barrel nut and slide your rail on and tighten the rail screws. It features M4 Feedramps, .2795 takedown pin holes and lazer engraved T-marks. Comes assembled with Port Door and Forward Assist installed. Includes dust cover. Finished in Magpul FDE Cerakote. Please Note- The M5E1 Upper Receiver is specifically designed to be used with our M5 Enhanced Handguards. It will not work with other AR10/308 handguards. Torque to 65 ft. lbs. with a standard AR15 Armorers Wrench.