Hub Rings.

More and more often, hub rings are lost or damaged during the assembly or disassembly of the wheel. With Unimotive's complete assortment, you now have quick access to the right set of hub rings. Sinatec Europe keeps more than 270 types of Unimotive hub rings in stock, which fit the most common vehicles. To prevent imbalance, be sure to remove dirt and deposits from the hub and wheel rim before mounting the hub ring and the wheels.

Hub rings, also known as centering rings, are designed to make an alloy wheel fit snugly onto the car's hub.
The smallest size indicates the hub diameter and is specific to the car, The largest size indicates the inner diameter of the wheel. 

 Download the overview here