i went down the same path. there are officially 4 different sizes! Only 3 in the US though from my search. Multiple sizes available in same years Best bet is to take a open ended wrench and keep going down in size until it won't fit over the sway bar. Or just put on some R32 front sways at the same time.
Don't forget you need to either replace the front sway bar or cut out the plastic "squeekers" on the original sway bar and step down 2 mm on the bushing. If you don't do this the whole frustrating experience will have to be redone and you will still squeek over speed bumps etc MJM doesn't sell the smaller 19mm suspension techniques poly bushing you will need if you have a 21mm and cut out the squeeker. If you have a 23mm and cut it out you should buy the 21mm.