Trying to i.d. this wrench (see url below). I've found similar wrenches in reproductions of vintage manuals, but not this number. I've this number listed as specialty tool within a 1930 Finish Ford catalog at the url below.
I forgot to add that the wrench is 6" wide, 6 3/8" long, and has a hex opening that was likely made for a 1/2" nut (17/32" exact inside measurement).
The 5Z-1821 is used for 1/2 hex head screw. According to my literature.
Interesting Swedish/Finnish parts price list!