Wesley, there are three sizes of the men's black faced Speedmaster chronos. The smallest is the Speedmaster Reduced automatic (model 3510.50) at a girly-manish 35.5 mm. Then there is the Speedmaster Day Date automatic (model 3520.50) at an intermediate 39 mm. The classic Speedmaster Moon Watch (model 3570.50) is a large 42 mm in diameter, but it's a hand wind model. For reference, a Rolex Submariner is 40 mm in diameter.I tried 2 omega speedmasters last night at the local jewelry store and im surprised
at the diameter.. they are a bit on the small size.