Well, F.W. Keler surpassed 29k post 1912 and it could be several thousand less when the new rules were implemented, so he seems to be out. Let's chase JCM for a time being either a mechanic J.C. of Mehlis, which is highly possible or mechanic J.C.M. Although I have seen any specific test of strength for Heinrich Ehrhardt's hollow cavity vessels, I'd say they would be pretty stout for fluid compressed steel. The initials on the right flat seem in reverse.

Kind Regards,

Raimey
rse