This Hogue OverMolded free float forend for the AR-15/M16 is sized for rifle-length gas systems (approximately 12 1/2 in from the rear of the gas block to the front of the receiver), in Flat Dark Earth. It works with all barrel types compatible with a standard Delta ring, fits older AR/M16 models with a triangular handguard, and is not compatible with piston gas systems.