Faria Beede Instruments Euro White 4" Tachometer - 7000 RPM Gass - All Outboards. 375" (85mm)Electronic tachometers work by counting pulses generated by the ingition 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 postion you let the tachometer know how many pulses are sent per each engine revolution.Benefits:Wide range of scales Multiple signal sources Rugged Reliable construction Specifications for Faria Beede Instruments Euro White 4" Tachometer: Manufacturer: Faria Beede Instruments Color: White Features of Faria Beede Instruments Euro White 4" Tachometer Wide range of scales Available for gas or diesel engines Multiple signal sources Rugged Reliable construction 4" - Hole size: 3.375" (85mm) Package Contents: Faria Beede Instruments Euro White 4" Tachometer Faria Beede Instruments 32905: Euro White 4" Tachometer - 7000 RPM Gass - All Outboards