Anyone that has ever fought one of these will appreciate this. There is nothing more frustrating then trying to get one of these off to put fuel in or check the level. Here is a simple solution we came up with. Billet thread on the cap features an o-ring seal and uses the same bolt pattern as the red plastic ones. The bolt center is 4.375 on the 6 bolt model. The bolt center is 5.400" center to center for the 12 bolt.