Question does anyone know off hand what thread pitch was used on pocket watch cases and if how many variations there might be sizes 18-12 tia

The thread pitch variations of 12-18s pocket watch case body/covers is as variable as the world population of fingerprints.

In short, the dimensional/mechanical quality control of case manufacture and fitment is ZERO!

You will find that even when a case cover MIGHT fit another case, usually the seams are mis-matched and very often the lead threads prevent full closure and always lose registration of the decorative case engraving or embossing.

Oddly, the most consistent case parts were probably those made for dollar watches which just "snap" together.

we're talking pitch not outside dia. are the threads per inch or mm pretty much the same on mfg's I am not looking for case to case fit just need to find out about tpi