Although the 'metric' direction that this thread has taken is a bit off topic, I would like to continue on in that direction. To me they are really only numbers, no matter which system is used. I will grant you that I have gotten comfortable with wrenches and sockets in metric, as I have dealt with Mercedes diesels for over 50 years. But as an engineer in the chemicals and petroleum field, I see no advantage to the metric temperature scale. In fact it is way too coarse when compared to the good old farenheit scale.
Also many modern autos purportedly made in the USA have a mix of inch and metric fasteners already, so just grab another wrench..... There is also the 2-liter bottle so fondly used for soft drinks, and the gallon - half gallon sizes for milk. Big deal, just numbers !!!