Metal alloy constructed for great durability. Compatible with most M4 and M16 AEG rifles. More stable than archaic multi-piece design that gives an authentic look. Capable to be used as a replacement upgrade over stock barrels. Includes all necessary parts for installation. In the Box 1X Outer Barrel Specifications: Manufacturer Krytac Build Metal Alloy Barrel Length 5 in Threading 14mm Negative Threaded Barrel Compatible M4 and M16 AEGs California Proposition 65 Warning: Cancer and Reproductive Harm - www.P65Warnings.ca.gov