Professional Red 4" Tachometer - 6,000 RPMPerimeter-lighted Black dial with stylish Red and White graphics, Black aluminum bezel, tear- drop White pointer, and flat glass lens.Electronic tachometers work by counting pulses generated by the ignition system, alternator, tachometer signal generator or magnetic pickup sender. The tachometer is hooked up to +12vDC, Ground and one of the signal sources.4"- Hole Size: 3.375" (85mm)Specifications:. Flat Glass Anti-fog, Scratch Resistant Lens. Black Aluminum Bezel. White Numeric Values with Red Increment Indicators. White Tear Drop Pointer. Factory P/N TC9933*Sold as an Individual**Gauge Cover not Included