XS Sight Systems Big Dot Sight Tritium Green S&W J Frame/Ruger SP101/Fixed Rear. Precision machined in Fort Worth TX XS Sights feature a patent pending glow dot that absorbs light and glows in low light levels before it is dark enough to see the tritium. Optic Orange is designed to offer a high-contrast sight picture when shooting in bright light conditions and maintain its visibility in decreasing light levels. To ensure visibility in low light when uncharged optic orange is primarily based on yellow with a hint of red. The increased surface area of the convex dot increases light absorption intensifying the charge of the glow properties of the dot. Big Dot demands your attention - even in high stress and for those with poor eyesight aids in rapidly achieving combat effective hits. Day-Light Half-Light or Low-Light place the bottom of the dot in the bottom of the sight channel and center the dot over your target within 15 yards. Outside Diameter Big Dot 0.188"; fits in common holsters. Fits S&W J-Frame with pinned front sight and Ruger SP101 with a fixed rear. Installation requires a drill press to drill the retaining pin hole in sight body. Specifications for XS Sight Systems Big Dot Tritium Sight Smith & Wesson/Ruger: Manufacturer: XS Sight Systems Gun Make: Smith & Wesson Ruger Gun Model: Smith & Wesson J-Frame Revolver Ruger SP101 Color: Black Gun Type: Pistol Illumination Type: Tritium Condition: New Package Contents: XS Sight Systems Big Dot Tritium Sight Smith & Wesson/Ruger XS Sight Systems RV-0003N-3Y: Big Dot Sight Tritium Green S&W J Frame/Ruger SP101/Fixed Rear