Spigot Rings (Centre Rings) are used to ensure that an alloy wheel is correctly centred on to the hub of the vehicle. If an alloy wheel is fitted without spigot rings it will probably cause the wheel to vibrate, make it almost impossible to balance, increase uneven tyre wear and in time will work the fixings loose. So, fitting wheels without spigot rings can be very dangerous.
Unfortunately most wheel manufacturers use different size spigot rings for their particular wheels so there is no "one size fits all" available
In order for aftermarket wheel manufacturers to cut down on the amount of different wheel part numbers they produce they use spigot rings to adjust the centre bore of the wheel (centre hub fixing hole) See Fig 1 and 1a.
This cuts down on the amount of different wheels customers need to stock and by changing the spigot rings a particular wheel can be fitted to a wide range of different vehicles.