The Big Dot Tritium front sight improves sight acquisition speed and tritium enhances Low-Light use of the defensive shotgun. Glues over front bead and the bead must be 0.120"-0.140" in diameter. It may require opening up bead hole to larger size by drilling & tapping. Fits Mossberg, Remington and others with bead mounted directly to the barrel. The XS Big Dot Tritium Front Sight is a stand alone solution and does not work with any rail or Ghost Ring solution.