Certainly true that some Italian pipe threads on seventies Italian
motorcycles are the same as Imperial. Why not? Britain and Italy had imperial
ambitions realised so why not threads in common? To muddy the waters even
further, B.A. threads (British Association) which go back into the nineteenth
century were originally based on a metric system. Confusingly, Morris in the
twenties used Imperial and metric which Ford in the sixties must have thought
was a good idea as for a while you could find Metric, BSF/Whit and UNF/UNC on
the same car. Recent informed opinion seems to think that the Whitworth
thread form got it right. None of which has much to do with bikes. When did
the threads on cycles begin to be standardised? I believe the Cycle Engineers
Institute threads were formulated in 1902. Did America follow suit? Or did
you take a leaf out of the Cadillac automobile company's and the Waltham
Watch Company's books and make up your own?
All this is off the thread but about threads so perhaps admissible.
Stuart Tallack in Sussex where I use metric, Whit, BSF, BA, Cycle,
BSP, Metric, UNF, UNC and BSA but still can't fathom out the threads that are
supposed to hold on a tachometer made by the Jaeger Watch Co. Inc. of New
York.