Fishy I don't think that you want to put an impact on these. They are tiny. All of them that I have seen are a 10 mm nut. What's up with that? :angry7:
I didn't know they were that small but a small impact (if you can get it in there) set on low might still be better than using a wrench. The problem I've seen with rusted exhaust studs/bolts is they generally twist right off when using a wrench or socket where-as a impact's hammering action doesn't twist things off as easily. That's been my luck but then again I have never tried it on a stud so small.