The Brite-Site TFX features fully-protected TFO technology encapsulated in a virtually indestructible configuration, impervious to oils, chemicals, cleaning solvents, and ultra-sonic cleaning processes. These sights provide unmatched visibility in all shooting conditions, 24/7, utilizing Swiss tritium for maximum brightness. Glowing in the dark without the use of batteries, the concealed fiber cannot be seen by target. Additionally, Tru-Glo's Fortress Finish provides a permanent protective coating for maximum protection and this snag-resistant design fits standard holsters. This model is compatible with FNX 40.