Here is a post by Cletis with general information - RIP, Charlie (we remember you)

DADS50 posted a key "socket" (code on bottom "stem) - see attached image, below.
I think that I have some old keys with the code on the key.

Charlie also had a long chain-ring with sample keys ("try out keys" used by a key smith to try to find a matching key for a socket).
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