I just bought a motor meter - question there is one rubber washer supplied and a nut. If used with the gull wings, does the washer go between the meter base and the top of the gull wings, or on the underside of the gull wings with the nut? then, any need to use a lock washer or some thread retainer?

John. The washer goes in the radiator cap and then the nut is tightened down to hold it all together. That is all that I use is the washer and nut. Dave.

Thanks Dave - I just went down and put it together your way! Thanks again.

Some of the old moto meters had a gasket under the meter. If yours is old you will see an indention where it would fit. Besides the rubber gasket I would place a washer between the nut and gasket, so the nut has something to bite into, if you go that way.
MarkG

I have a rubber "O" ring down at the bottom of the filler neck in the radiator and my Motometer screws down against that and I get about 1/3 turn more as it tightens in position. This keeps antifreeze off the paint and keeps the heavy Motometer form moving around.

I agree on the position of the washer.

Jim