The Bobro Engineering Double-Decker rail riser is designed to supplement an existing rail, giving you 5/8" of additional height. It is very stiff, and the cantilevered end has a tapered reinforcement rib so that it cannot flex even under severe use. The bottom clamp portion uses 10 cross slots on a Mil-Std 1913 Rail. The base permits the use of back up iron sights on the AR15/M16 series of weapons if desired. It weighs 3.3 ounces, and is constructed from 6061-T6 Aluminum and uses Grade 8 fasteners.