Originally Posted by cruzinquick

I have a set of 15mm and 20mm. I have both for my drag radial sets. The sets didn't need them to fit under the car, but the wheel I used was thinner than the stock wheels where the bolts went in. So best case is to take the wheel your trying to put on and see how many threads are left. Rob had told me that 7-8 were about what was factory. If you have more count how many more and measure that in mm to determine your spacer. If you have less than you need a longer bolt. I bought a set of ebay and cut them to stock length to have an extra set. The 20mm required I cut them a tad longer. Hope this helps.