Biagio, without going into a 50 page history of spanners (yes, they are spanners, NOT wrenches) in the past, there were dozens of ways of measuring bolts and nuts, hole diameter, bolt diameter, size of circle the nut was shaped from, etc etc. and every manufacturer made their own and sized their own, to make customers have to buy parts from the makers. So around the end of the 1800's a Mr. Whitworth attempted to standardise them all, which is where the "whitworth thread" came from. Which then became British Standard. But of course even then we has BS coarse, BS fine.
He was quite successful, but then the Uk learnt about metric and it all went to hell again.
And I havent even touched on the american SAE, and others because america is still only about 25% metrified (if that).
To make it even worse, this musclechuck nut measures 1"AF Which is stands for Across the Flats.
60 years ago when I first started using spanners on my motorcycles, I always though AF stood for American Fine thread, which just shows how screwed up things are.
Its hell out in nut and bolt land.