This Yankee Hill Front Flip Sight Tower with Bottom Rail adds the convenience of a flip sight along with the versatility of a bottom picatinny rail. The flip sight is easily concealed with the push of a button and locks in the deployed position. This Front Flip Sight Tower accepts all standard AR sight posts and hardware (included). The picatinny bottom rail is great for laser sights and flashlights. The Sight Tower's two-piece design allows it to be mounted on firearms with pinned and welded muzzle accessories. It mounts easily and securely with four cap screws using a 7/64 inch Allen wrench. These gas blocks have a bore diameter of .750 inches and are made of all steel construction for superior strength in demanding conditions.