Luth-AR 5.56 Mark 12 Barrel Rifle 1-9 RH Barrel Twist 1/2 x 28 Black. Luth-AR 18 in Mark 12 Barrel 5.56 mm will fit the bill. Specifications for Luth-AR 5.56 Mark 12 Barrel: Manufacturer: Luth-AR Color: Black Finish: Phosphate Fabric/Material: 4140 Chrome-Moly Caliber: 5.56x45mm NATO Barrel Length: 18 in Barrel Profile: Government Gas System Length: Rifle Length Gas Block Journal Size-Diameter: .750 in Threads per Inch: 1/2x28 Barrel Twist Rate: 1-9 Barrel Material: 4140 Chrome Moly Vanadium Flutes: No Gun Model: AR-15 Weight: 2.11 lb Features of Luth-AR 5.56 Mark 12 Barrel 6 Lands and Groves M4 Feed Ramp Button Broached Package Contents: Luth-AR 5.56 Mark 12 Barrel What firearm models does the manufacturer say Luth-AR 5.56 Mark 12 Barrel is compatible with? The manufacturer suggests that Luth-AR 5.56 Mark 12 Barrel is compatible with AR-15Luth-AR BL-M12: 5.56 Mark 12 Barrel Rifle 1-9 RH Barrel Twist 1/2 x 28 Black