I am looking for a compression gauge/leak down tester in preparation of recieving a 1990 cbr600f. I've read that I should check compression of the engine so that I know whether or not I'm wasting my time working on it.

Does anyone know the size of the spark plug holes in millimeters? Motion pro sells a kit with a few adapters( 12mm 14mm etc.). I would like to save money and find a single size adapter and gauge. Thanks for any help guys.