YHM - Folding Front Sight Gas Block W/Bottom Rail. This sight adds the convenience of a flip sight along with the versatility of a bottom picatinny rail. Available with either a round hooded front sight guard for fast and accurate sighting or a standard style front sight guard. The flip sight is easily concealed with the push of a button and locks in the deployed position. This sight accepts all standard AR sight posts and hardware (included). The picatinny bottom rail is great for laser sights, flashlights, etc. This sight'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" Allen wrench. For use with .750 heavy barrel only.