Copper for sure.  Pretty sure this was discussed in the last three months
and sources/links provided.

On Mon, Mar 31, 2008 at 6:52 PM, Ryan Shawley <easywind1975@hotmail.com>
wrote:

> So could I get a few of the list gurus to weigh in on this issue?  Should
> one use copper lock nuts on the exhaust studs, stainless, or the standard
> ones that typically come in a hardware kit.  I've checked the archives and
> their just wasn't a whole lot about it.
>
> Ryan
>

--
Jake
1984 Vanagon GL
1986 Westy Weekender "Dixie"
Crescent Beach, BC
www.crescentbeachguitar.com
http://subyjake.googlepages.com/mydixiedarlin%27