The Dirty Bird 7075-T6 True Mil-Spec Carbine Receiver Extension is an excellent choice for your next AR-15 or AR-308 build. The unit is machined from American 7075-T6 Aluminum to Mil-Spec dimensions and then finished with a Type 3 class 2 hard anodizing. The tube features 6 adjustment positions and drain holes per military specifications. American 7075-T6 Aluminum Held to mil-spec or better tolerances 6 Adjustment Positions Also available in Magpul FDE, OD Green and Midnight Bronze Cerekote. Backed by the Dirty Bird Industries, LLC Limited Lifetime Warranty