Details The AR15 Bar Barrel Nut is used to connect BAR style handguards to standard threaded upper receivers. This product comes with 4 shims to properly time the gas tube with the upper receiver. Compatible with mil-spec threaded upper receivers ONLY. Includes: BAR Barrel Nut BAR Shim Pack (4 shims) Features: Material: Machined from Billet 7075-T6 Aluminum Coating: Anodized Black Torque with standard AR15 armorer's wrench Supports Mil-Spec AR-15 barrels with outer diameters up to .998†View BAR Barrel nut instructions here. 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.