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. The advanced Mepro FRBS sights are made of strong high-grade polymer and metal parts and are highly durable. Quickly and easily flip them into position when needed. Maintenance-free can be mounted directly with no modifications using a 2.5mm Hex key (provided). The instant spring-locked deployment mechanism will not slip break or deform. Sight pin elevation is easily adjusted without tools and the windage adjustment with positive detent locking does not require tools.