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How do you tell them apart from normal ones? Invoices say I've got two different types in my spares box. Don't say a magnet as they're all magnetic, even my easy to identify, black xtr ones.
Leave them out in the rain & see which one rusts?
Is there a desperate reason to know? They all do the same job, you'll use them all eventually. I'd presume the non stainless ones would be be zinc coated. Mordant solution would turn zinc black, assuming theres not a grease/wax treatment on them that would prevent the zinc reacting
I have a favourite bike that gets treated a little better than the others.