KELCH 7J200725 Quarter Turn 7 1/4" Long Vented Marine Gas Cap Works on the old metal fuel tanks for outboards, this gas cap does not work on plastic tanks. You need a fuel tank at least 7 1/2" deep for it to work, and the filler necks measure 2 1/4" to the outside, and the center openin is 1 1/2" across, not counting the openings for the lock tabs Known to work on Mercury, Johnson, Sears, and others