To do business with the US Military measurements must be metric. US cars, trucks, no problem, hard metric for ages. Major equipment manufacturers like Deere, Case, metric. After all, world markets and although the US is the largest market, small compared to ROW (rest of world). When I started working for Cat, it was a to help a plant Cat bought move into the metric world. The product they had just purchased was designed in Europe and had just completed conversion to fraction inch because that engineering manager couldn’t understand decimals let alone metric. So Cat hired all these drafters to convert the fractions back to metric so it could be built in 4 plants for different markets. That was before somebody discovered it had first been designed in metric and finally discovered the original drawings. In the meantime hundreds of thousands of dollars worth of parts needed to be scrapped because converting back did not always give the same dimension. Example 3 mm, goes to 1/8 inch, but convert back and do you go with 3 or 3.2? Or 10 holes equally spaced at 25 mm can end up spaced at 1 inch and converted back to 25.4 by one drafter and 25 by the drafter converting the mating part. Result, the holes don’t line up. I get PO’d buying metric hardware at such a premium while Caterpillar or Deere buy at an equivalent cost per kg because of the massive number used. Or why my Deere tractor is all metric but my Frontier mower is inch because it’s not really Deere and the short line manufacturer does not have Deere’s buying power to get a decent hardware price. And in France they tell Brits they can substitute 80 mph speed limit on the 130 kph Autoroute because when the Brits went metric, they couldn’t afford new speed limit signs so highway speeds remained English units. But now I wonder if those are International miles or American miles? And a plane flying at FL 350 is at 35,000 ft - surveying feet or international? And when crossing into Russia needs to climb to 10,700 meters, or is it descend to 10,600? Gonna crash.