metal is very close to the top surface, and a scratch can easily penetrate to it.
It is exceedingly easy to damage the top side of a disc. Too easy. I always thought that was a stupid design flaw... or perhaps it was intentional. Really, how hard would it have been to add a protective layer over the top? Is there any substantiated reason why they don't?
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-- Terry K --
30Gb Smoke / Toyota 4x4
30Gb Amber / Bounder RV
Pants first, then shoes