In any larger workshop over here there is one toolchest usually marked in some bright and ugly color, all the tools marked in the same color, containing "Zollwerkzeug". That is, tools in inch sizes. You rarely need them, but on occasion you come across something from the other side of the pond where your 8mm wrench would just damage the head of your bolt. But often you can also get the job done with a monkey wrench.

However, this means that really changing over to metric, meaning also using international standards for tools, screws, bolts, wires, etc., needs buying new tools and material. I'm not sure how many metric tools there are in a typical US workshop, but I can imagine that they are not too common at the moment.