I picked this set up at auction last Saturday. It is a war finish set and in very good condition but I don't know if it was supposed to have an extension. It appears to be relatively uncommon in the 3/8" size.
Nice find!!
Very cool. I only have ever found one Circle U Craftsman and it's a 3/8 drive 3/4 socket. When I was in mechanics school we had a ratchet just like that one and it was cool to use something that old.
Actually, I have no idea what the war finish is composed of as it does not rust. It does however, tarnish.
The wartime finish may have been a type of low grade silver plate. The wartime Vise-Grips used it when chrome became a war material.