I had a hard time finding the studs with 1.5 pitch on one end and 1.25 on the other end (in town at least, I'd say Greg V could get them). I ended up getting some studs that were 10x1.5 on both ends and used some 10x1.5 nuts.
The nuts are also tricky. Most 10x1.25 or 10x1.5 nuts are going to be like 17mm outer diameter. Try fitting that and a 17mm socket against a 3" downpipe. The OEM ones are very thin walled, 14mm outer diameter, so the wall of the nut is only 2mm thick. I couldn't find any, so I made my own by finding some other size that had a 14mm outer diameter, then drilling and tapping them for the size I needed. Custom nuts FTW.