JE Machine Tech Ultra Lightweight J-Series rails delivers unrivaled weight savings and durability when success is measured by the gram. FeaturesBarrel Nut and all mounting hardware included7 MLOK slots in the 3,6 and 9 o'clock positions offer versatile accessory mounting options5 slot Picatinny Rail Section for your BUIS (or other accessories)Type II Black AnodizedMeticulously crafted from 6061 T6 AluminumTorque Spec 35-45 ft/lbThe wrench size for the barrel nut is 30mm