Ultimate Arms Gear Universal 12/20 Gauge/Shotgun Glowing Green Line Plain Barrel Front Fiber Optic Sight Bright High Visibility Glowing Fiber Optic Green Sight (Fiber Diameter 2mm or .078") - No Batteries Required. Quickly & Easily Snaps In Place Behind Factory Front Bead On Plain Barrel 12 & 20 Gauge Shotguns Notch in base uses the factory bead to locate the fiber optic sight correctly along bore axis Ultra durable construction & low profile design An Excellent Tactical Upgrade For a Home Defense Shotgun - No Gunsmithing Required