Indide/Outside Diameter
Dear William of Crossville,I had recently replace one of our dorad vents that suffrered decapitation due to a fouled jib sheet.

Ours is a 376 but I venture to say the same vents are used depending on the model year.I did get a standard vent from one of the biggie marine dealers. The Inside Diameter of the hole through the deck, or the outside dimension of the vent fitting itself, is probably the catalog listed size. The dorad vents snap into the deck fitting and they are standard. I do believe that 4 3/4" was our correct size.West Marine and Boat US are pretty good about letting you buy it and try it, so long as you don't ruin the produce the carton and the carton contents.good luck