That one is $40. The small bolt expands the reamer to the correct starting size. It only goes in one way. Then, the larger one is used to turn the reamer to strip away the ridge. There is a pad on the blade that scoots around the good part of the cylinder so that you can't go too far, although take it slow so you don't have to worry about it. I haven't looked, but I imagine there are YouTube videos on how that works.
