This is a Trijicon Sight known as the HD XR, model GL601-C-600835.
TRIJICON HD XR NS FOR GLK 9/40 YELL: Building on the features of the current HD(TM) Night Sights" the Trijicon HD XR(TM) 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" expedite engagements and see location of hits on target at longer distances.
Features:
Expanded field of view
Enhanced front sight acquisition
U notch rear sight
Tritium-Phosphor lamp
Protective aluminum cylinders
Sapphire window
Silicone rubber cushion
