This is a Trijicon Sight known as the HD, model GL113-C-600784.
TRIJICON HD NS FOR GLK42 YLW FRONT: The HD Night Sights were specifically created to address the needs of tactical shooters. The three dot green tritium night sight set's front sight features a taller blade and an aiming point ringed in photoluminescent paint while the rear sight is outlined in black and features a wider U-shaped notch.
Features:
Tritium-Phosphor lamp
Sapphire window
Protective clear coat and high visibility colored front sight post
U notched rear sight
Silicone rubber cushion
Subdued rear sight
