yeah i noticed that too........the different sizes and or adjustable ones.
i think you only need an adjustable if your running certain clutches and need to change the travel of the fork....as mentioned earlier, 50resto carries the stock or standard one, which if your using a stock, or king cobra type clutch will work just fine........did on mine anyway.....sometimes bellhousings will come with them already in it if it's used......unless you have the bell but no pivot stud
It's a little mushroom shaped ball on a stud in the bellhousing. You can't miss it because it's the only thing in it. The clutch fork rides on it. D&D Performance has them for $10.