This rear sight attaches to M16/AR15 flat top upper receivers. This site may be used as a back-up rear sight or a light weight rear sight to co-witness with red dot or holographic sights. The windage is adjustable using a standard A2 windage adjustment drum. One click allows 0.50 moa change on fires and 0.65 moa change on carbines. Constructed of both black oxide carbon steel and black anodized aircraft grade aluminum.