When installed on a vehicle, hub centric wheels are located directly off of the center flange of the brake drum or rotor. This means that the outer beads of the wheels are concentric with the wheel bearings which creates a much better balanced wheel and tire assembly. Aftermarket wheels usually have a standard center bore size to accommodate a wide variety of vehicles. Hub centric rings are rings that cover the spacing between the center bore of an aftermarket wheel to the hub of the vehicle. Hub rings are important because they secure the wheel in place and help prevent any type of vibration issue.There are different sizes of hub rings and they are measured in millimeters which are available through the dealer who sold the wheels.