The MBUS (Magpul Back-Up Sight) is a low-cost, color injection molded, folding back-up sight. The MBUS Front Sight is adjustable for elevation and fits most 1913 Picatinny-railed hand guards. Made in U.S.A. Impact resistant polymer construction provides light weight and resists operational abuse. Spring-loaded flip up sight easily activated from either side or by pressing the top. Detent and spring pressure keeps sight erect but allows for unobstructed folding under impact, etc. Clamps to most any MIL-STD-1913 Picatinny/STANAG 4694 railed hand guards and provides the same height-over-bore as standard A2 irons. Protective wings shield the spring-locking A2 front sight post. Elevation adjustment tool included, but most aftermarket A2 front sight adjustment tools may be used as well. NOTE: Cannot be mounted to a railed gas block due to excess heat issues. Front MBUS must be mounted to a railed fore end on the same plane as the receiver rail. Because of this the sight is also not compatible with MOE Hand Guards.