Can be used as primary or back-up sight Ergonomic 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 acquisition Dual 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 conditions 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 windage adjustments, with positive detent locking Made of extremely durable high-grade polymer and metal