Our Low profile Clamp-on style quad rail gas block is constructed of anodized aircraft grade aluminum with a glossy finish. The low profile gas block replaces the existing A2 front sight. It comes equipped with 4 picatinny rails 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 compatibe with 5.56/.223 with a .750 diameter barrel. Roll pin & set screws are included. No modification to your barrel is required.