I assume the 50/60 thing was caused by "MacArthur". Why the Yanks want to cling to the Imperial system to this day is beyond me. I loath it and why anyone would buck transition to the the International System is just... beyond me. Yes, it costs a few bucks but the USA doesn't dictate to the world any more with a trade deficit and a monthly due date it may not be able to meet. Just odd to me that Yankee commerce as a whole didn't see it looming as a "cost" in the long run.