The Yankee Hill Low Profile Gas Block replaces the existing front sight and provides a simple, streamlined design that can be used to mount a rifle length forearm to a carbine length barrel. Available with either a two set screw mounting system (#335471) or a clamp-on style mounting system(#462151). The Yankee Hill Machine Low Profile Gas Blocks measure .950 Inches long and 1.5" tall. They are manufactured from high quality steel, then finished with a Mil-Spec phosphate coating. Does not include roll pin.