Stock DP is 60mm at the catback side. 60mm = 2.3622in. Most catbacks come with provisions for mating up to the stock DP.Stock DP is 2.5", IIRC. In case you end up having you go buy a reducer yourself.
Ah, thanks. As for the clamp, it depends where you live. My GTI is a desert car and that clamp loosened extremely easily and there was hardly any surface rust. Same for the rest of the underside of the car. But it's always better to be safe than be crawling underneath your car, expecting your exhaust to take 2 hours only to figure out you need to go find a clamp because yours rust-welded itself.Stock DP is 60mm at the catback side. 60mm = 2.3622in. Most catbacks come with provisions for mating up to the stock DP.
To anyone replacing a catback I recommend buying a new clamp (part# 1K0253141N, 60x90mm clamp) because the OEM clamp is often quite rusted and requires removal with brute force (read: cut it off). It doesn't help that from the factory the nuts on the clamp are facing up towards the floor making it difficult to get a socket or wrench on. Trust me, buy a new clamp and be prepared to cut the old one.