Ok, first of all, when you say metric or English, what you mean is metric or standard (SAE). By using the word "English", you put my brain straight to "British Standard, which was different them metric, and as far as I can remember, was what you needed to wrench on old Triumph's (car & bike), or BSA's, and Norton's, or any thing made in Great Britain I suppose. Now that I've said that, I'll say this. My 2007 Harley has metric bolts, my '78-1/2 AMF Harley had a couple of metric bolts. My wife's Honda, built in America, has metric bolt's. A lot of things still have both. As far as measuring goes, I grew up with inch's and yard's,, and although I can comprehend how metric has some advantages, I don't want to relearn, which is likely why America still doesn't go all in on metric. Football would be a whole different game, that's for sure. As far as guns go, the military and NATO have a lot to do with it, and so does the diameter of rounds. A .40 S&W, is actually 10mm in diameter, and there is also a 10mm caliber, both are semi auto cartridges. But different length cases mean they have to be labeled differently, for safety reasons, because they are VERY far from interchangeable, so things have to be precise