Hi mate.
If you are talking about the internal diameter - I had to swap a bearing a while ago, and got the wrong size the first time. Unfortunately I cant remember whether it was the 30 or the 32mm that was right. I got told that even with vin numbers etc, you cant know which yours has. However, afterwards I searched posts and it seemed that a few people with a GTI was one size. It made me think that the diameter varies between the mkv platform (R32, GTD etc.)opposed to varrying between GTIs. But then again I only saw a handfull of examples. Ill search my posts to try and.find the right size