Spun Silver 4 Tachometer (7000 RPM) (Outboard)Perimeter-lighted Silver dial with bold Black graphics polished stainless steel bezel contoured Black pointer and domed glass lens.Electronic tachometers work by counting pulses generated by the ignition system alternator tach signal generator or magnetic pickup sender. The tach is hooked up to +12vDC Ground and one of the signal sources listed above.By selecting the right tach and setting the switch on the back to the correct position you let the tachometer know how many pulses are sent per each engine revolution.4 - Hole Size: 3.375 (85 mm) Specifications:Domed Scratch Resistant LensStainless Steel BezelLED Illuminating around the Perimeter of the DialFactory P/N TC9004*Sold as an Individual**Gauge Cover not Included