Quick introduction: I have the crown, below, in my parts box. I had thought it was correct for a late 50's Seamaster 300 (CK2913) but now I'm not at all sure. Can anyone conclusively identify this crown?
That's something I'm going to struggle with - I have nothing to measure and no threaded bar that small that I already know the size of.
Can´t you use windings stems of your watches where you know the size or messure with a caliper? I think it will be important to know this parameter in order to make an educated guess.