This is a Hi-Viz Sight known as the LiteWave H3, model MPSN321.
HIVIZ(R) LiteWave H3 sight combines Tritium with their LitePipes technology for day/night performance with 24 hour illumination. Front and rear sight are green. 12 year Tritium warranty. Fits Shield models in 9mm" 40 S&W" and .45 calibers.
Features:
Green tritium front with white ring
Green rear
Sight visibility in all light conditions
Factory sight heights
