By the date of this catalog in 1930, Hamilton pocket
and wrist watch cases were still being produced by outside companies and co-branded. Here is the inside of the case back from the 1929 Hamilton Tonneau whose movement is shown above. The "H" means that this case was made specifically for Hamilton and cased in Lancaster:
I believe that the same was true for the other larger American watch companies like Elgin, Gruen, Waltham, Illinois, etc. I think Bulova watch cases were taken in-house before 1930.
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