There was a day, when I worked for a BMC dealer, that I was faced with Whitworth, SAE/USS, and metric fasteners all on the same car, 70's era MGs for example and Saabs with Triumph engines and SU carbs.
So when American mfgrs. went metric, I was ready for them. It turned out that Whitworth wrenches worked on the even-numbered metric bolts. I have long wondered what went on when they chose the bolt head sizes. They could have followed suit with the European and Japanese makers, but no... Was Snap-on in the background making sure we all had to buy new tools?
