Nm exhaust studs nut?

undefined How many nm should the nuts on the exhaust studs be tighten to?

thank you

6 or 8mm studs? 

Those nuts are crushing a hollow copper donut, so the tightening torque is not the same as a regular stud and nut arrangement.  I'd tighten them enough to crush the donut and affect a good seal, and then maybe a smidgen more, and stop.  

I have to measure, but think they are 6mm.

thank you all.