BMW's use copper nuts for the exhaust as OEM.  I think that the 
theory behind this is that the copper will "give" before shredding 
the studs, et al.  I will say that in removing the exhaust system on 
my 535i 4 times, (long story) the copper nuts do seem to have made the difference 
but were only usable once.  However, in the last install I also used 
ample anti-seize.

Greg

Gregory V. Robinson
ajax@why.net
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85 BMW 535i 157K  (BMW Digest)
85 VW Vanagon  135K   (Vanagon List)
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