What they do is locate the wheel in the absolute center of the hub on the car. They may take a little load off the wheel studs as well. They can be bought for most set ups, but this particular car has an unusual "floater" hub set up. Always test fit before you torque the lugs, crazy things somtimes happen in the mfg process, the index could be off on the hub ,or the wheel ! and you will end up bending studs or something of the like.