The Trijicon HD XR Night Sights were designed with law enforcement agencies in mind. Building on the features of the current HD Night Sights, the Trijicon HD XR night sights are for the next level of advanced target identification and engagement at increased distances. A thinner front sight post allows shooters to have a larger field of view which further enhances the ability to identify targets and expedite engagements. Fits FN 509.