In fairness, I think you should know that my experience was with platinum plugs from aircraft. I don't know that I ever saw one from an auto----which I would assume would be much lower quality. Also, this was when platinum was under $400/ounce, so they were more likely to use it in larger volume. Long before the pressure on the platinum market for catalytic converters.
I recall quite well that there was a short length of round platinum for the center electrode, probably about a grain in weight. The ground electrode varied from manufacturer to manufacturer, although all yielded platinum. I figure about 10 plugs would yield a gram.
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