The Mepro FUBS is a tritium-enhanced set of sights two tritium vials are firmly inserted in the rear sight, and one tritium vial is inserted in the front sight. In addition, the self-illuminated backup sights are designed to provide the shooter with secondary sights if the primary optics go down. The advanced Mepro FUBS sights are low-profile, made of strong composite material, and are highly durable. Quickly and easily flip them into position when needed. Sight pin elevation is easily adjusted without tools. You can also use it as primary sight. The Mepro FUBS sights are mounted to any Picatinny rail using a 2.5mm Hex key (provided). A spring-based locking mechanism allows you to flip them into place when needed quickly. The detent knob on the rear easily adjusts windage, and the front sight includes an Indexed, easy-to-adjust Elevation Drum. No tools are required for zeroing.