I need some schooling.

[Northwoods]

Bought a Winchester double open end wrench at a farm auction today. 
It is all beef.  1 1/16" X 1 1/4".  This thing is 11 1/2" long and just a tad more than 5/8" thick on the big end.
But what I want to ask about is something most of you guys likely know.  Mine is designated W37.  I have never been very interested in the older double open end wrenches and only bought this one because of the Winchester brand.
Can someone link me up with an explanation of the letter/number identification codes?

[leg17]

37 is the Williams number that had been widely used as a standard.
Many makers used, and still use, the Williams-originated numbering schemes.

I assume the prefix W is for Winchester.

http://www.wrenchingnews.com/industry-standard-wrenches/chart.html