Originally posted by Digitalwave
It's called a centering ring... it goes on the car's hub and makes up the difference for a larger centerbore on the rim.
Actually its called a HUBcentric ring. Well atleast thats what American Racing calls them.
And they do need to made for the rim, it needs to fit the center bore perfectly or it wont be hubcentric. The whole point is to make up the difference between the bigger center bore of the wheel, and the size of the hub.