The MBUS (Magpul Back Up Sight) is the first of its kind: a sight designed as a low cost, color injection molded polymer, folding back up iron sight. The MBUS fits all Picatinny rail equipped weapons, but is specifically tailored to the AR15/M16/M4 platform. Dual aperature, adjustable for windage. Made in the U.S.A. $56.99