Just looked in the NGK book for a cross reference, but I can't find a WC7D. They cross reference Bosch W7D and a WR7D, but that's as close as it gets. Does anybody know what the "C" in WC7D means? Obviously the W7D is non-resistor type and WR7D is resistor type, but what is a WC7D? Copper core? Any Bosch plug experts out there?
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