There are different shaft sizes for the threaded portion of the shaft depending on what year model your car is and if you intend to use your stock ball you need to get the right thread diameter. 07-09 have a 12mm shaft, while the 10+ have a 10mm shaft. You need to select the right shaft size for your existing ball. I have both long and short shafts, so that is going to come down to personal preference. I like the longer one better, but we're only talking about 1/2".