That is a bushing. The bell you have has no pocket for the starter to fit into. The starter has a larger hole and the bushing locates the starter correctly. All bell housings should have the register dialed in. Your instructions state that in step 3. Every one I have done needed a correction. Once you get readings you can then determine how much of an offset dowel you will need. I use these as they are easily removed and adjustable. Dowels