It can’t be seen when the movement is assembled. On top it’s under the dial, and on the bottom it’s under the barrel, barrel bridge, automatic works and rotor.
The bottom of the screw is perfectly rounded and mirror polished. Maybe they did it so it would be less likely to seize up if there was any humidity entering the case, maybe to prevent it from cross-threading, I have no idea. It’s beautiful though. One of the first lessons I learned in Industrial Design was to find the parts that the end user is least likely to see, and make those parts beautiful. Design is not assembly purely for functionality, it is a sauce. The ingredients matter.
Most of the time when I break something open to fix (electric razor, computer, motorcycle), the insides look like a poverty stricken shanty town for ants. Full of tape, glue, messy welds, scratches, engineer graffiti and bits thrown about like a musty storage warehouse. Watches and clocks though, it’s a different world.
