This backup plan is always in sight. The Mepro FRBS is a tritium-enhanced set of sights – two or four smaller tritium vials, depending on the model, are firmly inserted on the large aperture side of the rear sight. The self-illuminated front and rear backup sights are designed to provide the shooter with secondary sights in case the primary optics go down. In addition, the Front Sight post elevation is easily adjusted without tools. Day or night, the tritium makes the Mepro FRBS a viable option. The Mepro FRBS is an advanced, dual aperture, durable and low-profile auxiliary tritium-enhanced set of backup sights. 4 tritium vials are firmly inserted in the rear sight, and one tritium vial is inserted in the front sight. In addition, the Mepro FRBS self-illuminated backup sights are designed to provide you with secondary sights if the primary optics go down. You can also use it as primary sight.