Oh, hey, sorry I didn't see this until now. Here's how it works - you have holes in metal bits. You have a metal sleeve that goes in the bushing. The hole is bigger than the sleeve. Therefore you have the nub to fill the gap for the hole. The reason is this - you need the sleeve so that the bolt doesn't "saw" through the bushing due to vibration, but at the same time you don't want the sleeve right on the edge of the hole because it will vibrate. Thus why you have the nubs.