Can 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, webbing, or brushInstant spring-locked deployment mechanism will not slip, break or deformNo tools needed for easy, rapid windage adjustments, with positive detent lockingMade of extremely durable high-grade polymer and metal