Tube and stem size of bowler hat crown for Seamaster ref. 2869?

Have you measured the tube on the watch? That's probably the more relevant info. It might have been replaced in the 60-odd years the watch is old. Measure the tube, measure the tube opening of the crown in question, there you go 😀 The 501 stems are all the same size (and are cut in length according to the requirements).

As you know, I also replaced the crown on my (formerly your) 2869 to a bowler hat example and actually had the tube size changed to make the crown fit.