Albert, thanks for the detailed background on spark plugs. One can learn a lot from design engineers.

I've always taken a file and rounded down the corners of my spark plugs - not the corners facing the center electrode, but the two upper corners and side corners... made it shaped somewhat like the end of a twinkie. I guess I was doing it to focus the charge for the spark and to reduce any unnecessary hot spots on the electrode. Have I been harming anything?

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95 E320 Cabriolet, 169K