Machined from 6061 T6 aluminum and incorporating the 1913 picatinny rail on top, These new gas blocks have a pleasing angular profile and an additional set screw on the top surface to insure a perfect gas seal. The blocks are hard coat anodized and are shipped with 3 set screws. Available for Lightweight (.625), HBAR (.75), or Bull Barrel (.9375) Not recomended for full auto aplications.