I haven't been lucky with them. I had to replace most of them. A mechanic helped me, because some holes needed a timesert, a method he prefers over helicoil. On his advice I used but OEM studs and not ss. When either loosening or fitting the exhaust system, be very, very careful with tightening (or loosening) everything. I wish I could give you the right working order; opinions seem to vary. Do not use a torque wrench on those 8 6mm nuts. It will work well only once and thereafter you may encounter problems.
Later models had ubs nuts which do not need spring washers. I haven't tried them yet. They may be better for the job, but they offer a little less grip for your spanner ofcourse.