as I recall spark plugs were invented overseas in England that's why they are metric??
Of course....... I don’t think England was on board with the metric system “back in the day”.
Hey ...we still aren't
Actually, we're kind of schizophrenic - still universally use miles and mph, milk sold in pints (let's not go there...), sometimes use lbs weight....but at school even oldies like me did all my maths, and Engineering degrees in metric, and pretty much everything else is metric too. I'm just about used to deg C in the weather forecast....but I speak deg F too
