FAB Defense FXRBS Rear Back-Up Sight for AR-15/ M16/ M4

The RBS is an advanced, low-profile, durable, auxiliary rear sight. It can be used with any front sight, but has been designed to provide an extreme optical advantage. It 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 front sight. The low folded profile is smooth and inconspicuous and will not snag on gear, webbing or brush. The 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. 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.