Meprolight USA 404100 Mepro FUBS Self-Illuminated Sights Flip-Up Green Tritium Front & Rear with Black Frame for AR-15 The Meprolight FUBS are tritium-enhanced, self-illuminated front and rear back-up sights designed to provide the shooter secondary sights in case the primary optics go down. FUBS sights are advanced, low-profile, durable, tritium-enhanced auxiliary front and rear back-up sights. The sights quickly fold up or down depending on the shooters needs. Sight pin elevation is easily and quickly adjusted without tools. FUBS sights are readily mounted on any 1913 Picatinny rail.