Hey what's up with the " 3/8" x 6 " on the adjustable? Is the "3/8" the jaw opening, or thickness of the head, or... ?
The only thing that I can think of is the 3/8” might be the thickness of the jaws. It is a 6” adjustable.
It's a German (and perhaps a European) thing that I only became aware of myself in December 2019 when I found this Miltex 1/4 x 4" adjustable crescent-type wrench, as reported and discussed on the Garage Sale thread.
I'm pretty sure I solved this riddle, guys, with the help of a Q&A up on the General board's 'Old World' thread.
Believe it or not, it looks like the fraction might be the maximum capacity of the jaws expressed in Whitworth standard. Similar to the way US mfgrs would stamp the U.S.S., Hex Cap, or S.A.E. bolt size on the face of a DOE wrench instead of the milled opening size.
I know, I know, a little strange, even for the Germans, for a wrench whose whole, implicit, and intentional point is to be wrapped around nuts and bolts of many different sizes. But if you picture a slew of them hanging side by side on a rack from smallest to largest, I guess it kinda sorta makes sense to see its maximum jaw opening on the shank and knowing you could work down from there.
Why Whitworth? I'm assuming they were aimed primarily at the UK market.
My 1/4 x 4" has a 9/16" max capacity, which does fit a 1/4W.
Your 3/8 x 6" should have a 3/4" (3/8W) max capacity, Don.
And your 5/8 x 10" should have a 1-1/8" (5/8W) max capacity.
Too impatient to wait until October and your annual trek from your cabin to the Dunlap shrine in the Den of Dandy Delights in your main domicile, I got a brainstorm. Based on the premise that by the 1940's and 1950's the adjustable wrench would have settled into a globally appropriated optimal design, I measured a bunch of my 6- and 10-inchers made by several different mfgrs.
Sure enough, they are all 3/4" and 1-1/8" max capacity respectively.