The RBS is an advanced, dual aperture, durable and low-profile auxiliary rear sight. It can be used with any front sight and was designed for more accurate aiming and faster target acquisition. Windage is easily and quickly adjusted without tools. RBS is readily mounted on any 1913 Picatinny rail, making it ideal for use on M4 / AR-15 / M-16 platforms and on the FAB Defense K.P.O.S. Features: Can be used as a primary or back-up sight Ergonomic angel-wing-shaped front shroud helps center the image with any rear sight, but when used with a matching FAB Defense RBS Rear Back-up Sight, it creates a precise optical tunnel that ensures more accurate aiming and faster target acquisition Low folded profile is smooth and inconspicuous, and will not snag on gear, webbing, or brush Instant spring-locked deployment mechanism will not slip, break or deform No tools needed for easy, rapid elevation adjustments, with positive detent locking Made of extremely durable high-grade polymer and metal