Designed by Paul Howe to allow the operator to accurately engage targets from 7yds to 100yds without moving hands to flip sights or have a second set of sights. The notch on top is used for targets at 7yds with a sight picture similar to pistol sights. The aperture is used for targets at greater distances and is used as a normal AR-15 rear sight. Fits A2 Rear sight housing.