The Fab Defense RBS is an advanced, dual aperture, durable and low-profile rear backup 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. The RBS is readily mounted on any 1913 Picatinny rail, making it ideal for use on AR-15 platforms and on the FAB Defense KPOS. An ergonomic angel-wing shaped shroud helps center the image with any front sight, and when used with a matching FAB Defense FBS front backup sight, it creates a precise optical tunnel that ensures more accurate aiming and faster target acquisition. Features: 3mm and 1.5mm aperture for different light levels Instant spring locked deployment mechanism No tools needed for adjustment Low profile when folded, will not catch on gear or webbing