Speciatly rear sights for Glocks. I-Dot has single green tritium vial under notch. Ghost ring has two small tritium vials at the 3 and 9 o'clock position on the ring. Specialty rears should be used with 0.220" height fronts on 17192223242627333435373839 models or 0.200" height fronts on 202129303132364041.