Our High profile gas block is constructed of Anodized Aircraft grade aluminum with a Matte Finish. The High 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. It sits flush on your quad rail without any gaps. It is compatible with .308 with a .936 diameter barrel. Roll pin & set screws are included. No modification to your barrel is required.