FBS (front Back-up sight) is an advanced, low-profile, durable, auxiliary front sight. It can be used with any rear sight, but has been designed to provide an extreme optical advantage. Its sight pin elevation is easily and quickly adjusted without tools. The FBS is readily mounted on any 1913 Picatinny rail, making it ideal for use on M4/AR-15/M-16 platforms. The sight can be used as a primary or back-up sight and the ergonomic angel-wing-shaped front shroud helps center the image with any rear sight. The low folded profile is smooth and inconspicuous and will not snag on gear, webbing or brush. The sight is also made of extremely durable high-grade polymer and metal, and has an instant spring-locked deployment mechanism that will not slip, break or deform