This is a AmeriGlo Sight known as the I-Dot, model GL-305.
Utilizing a dot-over-dot configuration" their i-Dot sets have an extended square-notch rear for increased sight radius with a glare-reducing undercut rear face. The i-Dot sights provide a quick and easy vertical sight alignment" making it an excellent choice for all shooters.
Features:
Green tritium .140 wide LumiGreen outline front
Green tritium .165: wide notch rear
