The Truglo GLO Dot Universal is a fiber-optic front bead sight for shotguns. It is passive with no battery, gathering ambient light into a bright green dot through roughly 0.060 in of fiber-optic material. It clamps to ventilated-rib barrels and keeps a very low profile. Features: Fiber-optic front bead sight (passive, no battery) Green gathered fiber-optic dot, approximately 0.060 in fiber Clamps to ventilated-rib shotgun barrels Universal rib fit, any width or taper Very low profile For shotguns with a ventilated rib. Confirm your barrel has a vent rib before ordering.