Features: 1pc free float design Built in anti-rotation tabs Scalloped rails Continuous top rail 1.72" inside diameter (from barrel nut cut to forward end) fits most muzzle devices and 1.5" suppressors 1.78" inside barrel nut cut area diameter Compatible with low profile gas blocks Gen 2 Feature - Eliminated half of the 3, 6 and 9 o'clock picatinny rails, saving weight and providing a more ergonomic design in the rear gripping area Gen 2 Feature - Quick disconnect sling socket at the 3, 6 and 9 o'clock positions Gen 2 Feature - Additional milling along flats to aid with gripping and add visual appeal Gen 2 Feature - New profile for the continuous picatinny top rail Are you attaching this handguard to a standard threaded upper receiver? Make sure to select "Yes" under the Bar Barrel Nut option above (shims included). Our handguards use the BAR interface and do not work with a standard barrel nut. If you are using our M4E1 Enhanced Upper Receiver, no additional pieces are needed.