because the threaded shaft was too short to make it through the plywood, edpm liner with the nut tighten flush i had to recess the area 7/16". it took two hole saws one larger then the holding nut and one just large enough for the threaded bulkhead. first the larger hole saw first to score the area then use a router to remove the material and recess the large hole, then with the pilot hole drilled by the guide drill bit on the hole saw arbor the smaller whole saw is used to drill the shaft hole.