Please Note: All Aero Precision Handguards use the BAR interface. If you intend to connect an Aero Precision Handguard to a standard threaded upper receiver, you will need a Bar Barrel Nut. If you have our M4E1 Enhanced Upper Receiver, you do not need a BAR Barrel Nut as the barrel nut and rail mounting platform are forged directly on to the upper receiver itself. *Recommended torque settings between 30 - 45 ft lbs. Torque over 45 ft lbs may result in damage to the barrel nut.