Many aftermarket wheels and some OEM wheels require hub centric rings to downsize the center bore correctly center on the hub and to offer vibration free operation.
66.6mm is a common size for lots of 5x112 aftermarket wheels as this is the hub bore of many Audi and Mercedes fitments.
These rings downsize the wheel center bore to the 57.1mm center bore size found on the majority of VW vehicles.
Sold individually, 4 required per vehicle.