The 2 hole Rail Riser mount was originally designed to set on the M4 flattop receiver but it has proved to be a versatile base for many different purposes.
Rail riser is constructed of T6 6061 hard coated black anodized aluminum. The full 1913 rail is has overall length of 6.25" with 3" of overhang. The riser weighs 3.3 ounces. The aluminum rail lifts the mounting surface up .450" and allows the extension to the front or rear