Dial range: 0-7000 RPM Scratch-resistant domed glass lens. Enhanced illumination: through-dial and perimeter lighting for excellent readability at night. 3" tachometer/hourmeter (electric). O/B and 4-stroke gas engines. Mariner 30 and 40 HP (2-cylinder) engines require a module (Mercury P/N 17461A2) when using any of these tachometers. Not tested for non-original-equipment (aftermarket) ignition systems. Not for diesels. Sender code: O/B ALT./COIL. Cutout dimensions: 3-13/32".