I believe this wrench was first introduced with the Harley Davidson Knucklhead in 1936. It was also issued with the Panhead. I believe it is the rear axel wrench and i can not remember what side of the wrench is which. I am not a Harley guy, but this should give you enough info find out more. I have one , but with a new job and a new house I am not sure even where it is. If you have not found anything in the next couple of weeks, I will see if I can find mine. This was issued in the standard tool kit for the above motorcycles.
Thanks,
Kirk