mike–when I decided to gasket the aft edge of the hatch, I first used the 7/16″ thick size. that made the hatch bow out at the edges (with the hasp latched) telling me that thinner gasket would do. I removed the 7/16 and used 3/16. there is an impression on the 3/16 gasket from the molded rubber gasket telling me that it is thick enough.