Found this really useful when purchasing collets online: Scanned this chart from my "The Watchmakers and Model engineers Lathe" book by Donald de Carle
Scan.pdf
Err begs the question, If you had that sort of money & wanted that watch, would you not go to an extremely reputable dealer located in one of the more exclusive parts of a major city, or buy it off fleabay?
Some git will be flogging the crown jewels on there next, accompanied by the usual word - RARE.