The FAB Defense Deployable Rear Sight 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. The 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. FeaturesCan be used as primary or back-up sightErgonomic angel-wing-shaped shroud helps center the image with any front sight, and when used with a matching FAB Defense FBS Front Back-up Sight, it creates a precise optical tunnel that ensures more accurate aiming and faster target acquisitionDual apertures are 3mm for longer eye relief mounting, low light, and faster target acquisition; and 1.5mm for shorter eye relief mounting and greater accuracy; each is instantly selectable to match conditionsLow folded profile is smooth and inconspicuous, and will not snag on gear, ...