Dorton begins by seating his alignment fixture inside the rear main cap. It has been cut to fit inside the housing bore of the main cap and is slightly larger on the outside to fit the inside of the housing bore of the fixture perfectly. Then the bottom of the adapter (along with the gasket and a thin coat of silicone) is bolted into place, tight against the bottom half of the fixture. This aligns the center of the adapter with the center of the main cap housing bore. If this isn't done, the crank sits against the seal unevenly and you will eventually get a leak.