In the past there have been discussions about the alloy wheel bolts, were they clear cad or were they chromed. I would say 90 per cent I have seen over the past 35 years have been clear cad. Well I happened on on to some factory lugs that appear to have been chrome. You can see the copper base coat and some of the nickel showing on these bolts. I still think it goes back to who was supplying parts for that day on the assembly line.

As far as I know, all were copper plate on the steel, then cadmium on top of the copper.
The copper allows better adhesion for other metals on top of steel.