"Doug Miller" wrote in message
m...
In article , "JerryMouse"
wrote:

(snip)
4) The spark plugs most widely used in the U.S. have 5/8" or 13/16" hex
heads.

I think he was referring to the threads, not the wrench size to put them in.
IIRC, when Henry the First was setting up shop, there were no US spark plug
makers, so he had little choice but to use metric. Since he was the 800
pound gorilla, that is what the industry standardized on. I could be wrong,
of course, but I'm sure someone smarter than me will post the correct story.

aem sends...