Over the years I've acquired a bunch of these. I probably have more than a half dozen here and there. I've also give away a couple to a cousin who was a Ford Model A aficionado. The generic ones are pretty low in value if they have any at all, but when there's clearance they work well, and they open very wide. Once upon a time they were pretty much standard for any automotive toolbox. For the opening size, think of things like the big brass bearing caps that were once common on car front axles. A lot of old farm machinery, wagon wheel axles and the like, had huge square nuts.
The OEM Ford Model A wrenches were similar, but had a 1/2 inch square end on the handle for drain plugs. Ford tools will have the name in the familiar Ford script.