I'm lost............Wheel spacer's are sold in pairs (one for the driver side, one for the passenger side). Thickness varies in different millimeter sizes (i.e. 10, 12, 15, even 20mm, etc....) They are then mounted between the hub and wheel, hence the stud kit, as the added thickness now puts less lug thread in the hub which is unsafe. Any spacer run on these cars should also be hubcentric, as it will ensure that the wheel sits completely centered on the hub, much like as it would when stock..........please see reference photo below
Stock Hub....
Wheel Spacer w/Hubcentric Ring....
