Our Low profile gas block is constructed of anodized aircraft grade aluminum with a Matte Finish. The Low profile gas block replaces the existing A2 front sight. It comes equipped with picatinny rails on top and bottom allowing you to mount accessories such as a front sight or a laser underneath. The top rail is lower than the flat top by 0.28". It is compatible with .308 & 5.56/.223 Bull Barrel with a .936 diameter barrel. Roll pin & set screws are included. No modification to your barrel is required.