I think my exhaust studs are stripped like you describe.  I had the exhaust pipe off for repainting and bought a new gasket.  Installed everything and went to torque the nuts to spec and it feels like the studs are just spinning and I have a pretty bad exhaust leak.  I saw where the head holes can be drilled out and tapped to 8mm for using an 8mm stepped stud.  I assume something like this...?
 


 

Those don't look "stepped"?

Yamaha used the stepped studs on a few models from the factory... or a heli-coil or thread sert would work.

www.amazon.com/Step-Stud-31mm-Compatible...1?crid=1LCD1L11IH4JL

If it's stripped out at 6mm you could get lucky going to 1/4 coarse thread. Tap to that without lifting the cylinder & just use allen head screws/bolts. Get a tap in there using an 1/4 drive extension back to front to clear the frame & then spanner or tap holding handle. Just dodgy things i do!!.

Yamy did the 8x6 mm stud also? The Kaw was bad enough.

How completely wrong for design.
cliff

Yams 8x6 were back to front & had the 6mm in the hole 'i think'?, crazy idea anyway, but could use them tapped to 8mm with the 6mm sticking out, 'still dodgy-well maybe not & keeps it looking original'.
You'd need to have that Yamy stud right in 'at least flush' or the step will stop the exhaust flange going right home against the cylinder.
Not sure how much meat a 125 has around the stud hole but 8 is a long way from 6.

That's weird what am i doing wrong. If i bracket stuff early in the text & doesn't show the words in the bracketing. But the rest of the text goes italic or whatever ya call it. Then go back & remove brackets & it comes back all good.Just annoying me that's all lol. Not hitting anything on the keyboard & does it on other computer too. Sorry Rant Over.

I would probably do what RT325 says and tap to 1/4 inch might get lucky