I'm nearly positive that they are sized by the hose barb that 's on the through hull....so a 1" through hull has a hose barb that fits 1" id tubing.
The ones that drain my cockpit are 1". you should just be able measure the id of the tubing that goes to the one you want to replace and order it that way.
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1986 V-20
1986 Yamaha 150 HP
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