This tach was designed for use with Rotax and other 2-cylinder engines. Mounting hole diameter would be approx. 2.05-inch; exterior bezel diameter is ~2.4". The tachometer was previously fitted in an ultralight aircraft, but was removed when an all-new instrument pod was installed. I've sold my plane and don't have a way to test this tach for operation/can't guarantee operation or fitness for your particular application. The good news is the price... only a fraction of a new component from the same manufacturer. Please ask your questions before bidding!