While "1M.7z" looks like a modern compressed archive file (the .7z extension), its appearance in these records indicates a different original meaning:

If you found this as a digital file name, it is likely a modern archive containing data related to these historical "Morgenthau Diaries" or similar archival collections.

In a document from the FDR Library , the string is recorded during a conversation involving a "Miss Chauncey" and a "Dr. Viner." The surrounding dialogue suggests it was a reference used while discussing administrative or logistical "business" that needed investigation. Potential Contexts

In the mid-20th century, alphanumeric codes like "1M 7z" were often used for specific file folders, legislative acts, or internal tracking numbers within the U.S. Treasury or Executive Branch.