I'd say that Stillrunner nailed it. A JC Whitney type of almost looks like replacement that was half price of a new one from the dealer. This should be the original version. It might possibly be a base model cap for the same year or a truck cap for the same year though.
It's a Holden/export cap, check out this link which hopefully works http://home.znet.com/c1937/paint.htm This picture is shown and quote "The Holden (note the blue wheel and hubcap without "speed streams") had a different stripe pattern." Aftermarket caps wouldn't have the correct spelling of Chevrolet on them since the maker would have to pay to use the trademark.
Canada and Australia were both Commonwealth countries then, we got a lot of CKD's from Canada, so you would have ended up with Australian hubcaps. This was my car, '37 Sedan.