Magpul Industries, MBUS Back-Up Rear Sight Gen 2, Fits Picatinny Rails, Flip Up, Flat Dark EarthThe MBUS (Magpul Back Up Sight) is a low cost, color injection molded, folding back up sight. The dual aperture MBUS Rear Sight is adjustable for windage and fits most 1913 Picatinny rail equipped weapons, but is specifically tailored to the AR15 M16 platform. Features : Spring loaded flip up sight Spring loaded flip up sight easily activated from either side or by pressing the top Protective wings shield the dual, same plane flip apertures Detent