Most wheel companies will send them with the new wheels like Motegi for one. Some vehicles are lug centric which means when you tighen the lugs, the wheel will be centered and you won't get vibrations when driving. J-bodys are hubcentric which means the wheel has to sit on the hub for it to spin true. If you look at your stock wheels when they are on the car without the plastic hub caps, its sits on a circular disc. called the hub. The hub is also your wheel bearing assembly. The hub size is 57.1mm on j-bodies. So say you go out and buy a set of rims that are 10 lug universal and universaly bored. It is going to have an extremly large bore size to accomodate other cars that have different hub sizes. When i bought my wheels i didn't know about these, and just threw the wheels on my car no questions asked. I could only go about 40-50 mph before my whole front end shook. I thought it was just severly unbalaces but it was not. I did a little research and found i needed the rings. I called up the company that made them and asked for the bore size ( first time around some fucking Foreigner gave the wrong Size and i got the wrong rings, so i have 2 sets now and maybe even 3. ) THere should be no play in them when you stick them in your wheels. I have 73mm on my rims right now, but i have a little play so i might get 1mm larger. These rings fill in the gap between the bore of the rim and your Hub size. So if you get wheel vibs, these are what fix it. Even if its off just slightly, it can cause serious vibs at high speeds.