A round "o" in the word Plomb and marked "Los Angeles" with a year number followed by a letter dates it between
1927 and 1933. The single number would be the last number of the date. A point down triangle for the "o" in
plomb dates after that. I have no idea what tool your part came from, they made all sorts of tools, wrenches, sockets, adjustable end wrenches, hammers etc., including "Proto" tools in later years.