As Spencer said the ID is 3.5" and the OD to the edge of the flange is 4.25". They come with an adhesive gasket on the underside of the flange. They were a little loose on my Mobius until I peeled off the backing and stuck them in place.
LOL, mine did too! That is too funny. I just centered mine in the hole and stuck them down. I did clean the surface around the hole first. So far, so good. It really dressed the boat up for less than $50.