It's from the racing speedmaster. So it's 19mm.
The CK2998 is 19mm at the lugs, so is the FIOS. Neither of them were released with a bracelet, so many of us went with the racing braclet which is a more modern look. There is another braclet that gives more of a vintage type look, but it was not for me. I like this look much better.
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This look I like too.
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