The Mepro FUBS is a tritium-enhanced set of sights four 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). 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.