Wheel hub centric rings are designed to fill in the gap between the hub of the car and the center bore of the wheel. Most wheel manufacturers design their wheels with a centerbore large enough to fit on most cars. Therefore, since wheel manufactures make their center bore large enough to fit most cars, most wheel fitments have a gap between the hub and the centerbore. This gap usually doesn't allow for the wheel to fit in a hubcentric manner but rather lugcentric which causes vibration. Therefore, to fill the gap and ensure the fitment is hubcentric, hub rings are used. Circuits Sports offers these at a great value and are a great investment should you invest in a nice set of wheels.