There is also a rare variant of these double enders that was made on the old "S" handle adjustable wrench pattern. As you can imagine these are are a strange looking 'critter'. They were made by either Billings & Spencer or Bemis & Call. My memory fails me here. Also I haven't been able to find an image to post. Will keep looking for that.
Both Crescent and Diamond made the type you have in 4 sizes(that I am aware of). There is a 4-6, a 6-8, an 8-10, and the 10-12 like yours.
They were also available in two finishes. A bright finish, nickle/chrome, and black oxide like yours.
I was told by a fellow at a tractor show last year, that these were also made in a 12-15 version. Not quite sure I believe this, as I have never seen one, nor have I ever talked to anyone else who has. There is also no online reference to one.
Now you only have to get 7 more to have a complete collection of all that were commonly make.
Good Luck, Mike