I found this 8-inch Herbrand wrench today in the litter on my workbench. The openings are 15/16" (closed end) and 1/2" (open end).  It looks, from the typeface on the bosses, that the wrench was produced sometime before 1900.  It also appears to have been finished on a Monday, or by a novice.
The letter N is backwards in the words Herbrand and Fremont.  Also, the number 993, was botched during the embossing step.

The wrench appears to be designed for a specific purpose. Does anyone know what that was?

This is ringing a bell, but I cant quite get it.

could it be late enough to be a 'ford' wrench?

Skip

The stamping is likely in the forging die.
If a limited run, then the die was not repaired and all examples probably look the same.

More information on this 993 Herbrand wrench can be found on Alloy Artifacts. It is an early spark plug wrench. Note the backward N's on the Alloy Artifact photo.  Leg 17's remarks were spot on!

http://home.comcast.net/~alloy-artifacts/herbrand-van-chrome.html#herbrand-993

If you google 933 Herbrand wrench , you find the Backwards n is common.
Some were for sale on Ebay. Stated as spark plug wrench.