uncle mac I recently found a item exactly like yours .it is about 3/4 to an inch round and about 18 inches long.the pin off to the side 3/16 thick and 5/8 long with a round head on top that yours is missing.wish I knew what it was.
uncle mac the idea of a jack handle seem logical but mine has a nail looking spur on the side.i do have a jack handle but the spur is a lot shorter and the handle is semi hollow .but the answer birky quoted is not bad.