The gasket should cover all mating surfaces from inside edge to outside. I believe the material is 3/16" thick or there about. Rummy In a message dated 6/7/2013 1:20:02 P.M. Eastern Daylight Time, steverayj at hotmail.com writes: http://rhodes-22.1065344.n5.nabble.com/file/n45862/centerboardmineapart02.jp g