This is a cut/paste from an Art Thraen post on the CLF; his uncushioned (no radial springs) "Copperhead" friction plates have the normal friction material on one side and copper pucks on the other.
"Not exactly related but, As many know there are some of those
200mm 12Volt "New VW" CAST IRON fly wheels out there and they
have been known to break easy around the gland nut area, Well, A
customer of mine put one of my "Copper Head" Disc on the Cast iron
flywheel and The Copper Head Disc ate clear through the flywheel and
didn't even wear the disc. This happen in less then 5000mi. So stay
away form the CAST flywheels they are bad....and find the old german
Forged flywheels..."
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