Originally Posted by
grifone37
The British and Italians (whom the Japanese copied) used several inch-based ("English") threading systems that have the same threads per inch, but different pitches
I think you misspoke yourself in the underlined phrase. In my world, at least, "pitch" and "threads per inch" have the same meaning.
A general comment I have about this discussion; the basis for units of length, etc. in the "metric" or SI system are no less arbitrary than more traditional units. However, Napoleon's metric system has the enormous advantage of being conceived as a whole, rather than piecemeal over millenia, so it is much more organized and coherent.