My pleasure. One addendum on the "720" marking, which continues to fascinate me....
Even though Bonney, like many other mfgrs, adopted the Williams numbering scheme (whose high and almost unanimous adoption rate is why it became known as the industry standard), they also extended it - apparently some time between 1925 and 1933, which contains the year (1929) your wrench was made.
This will take some explanation.
Most DOE engineers wrench charts start at 721, which is a 5/16" x 3/8" wrench. Williams' own wrench charts in Williams period catalogs up through 1943 start at 721. I couldn't find a Williams catalog with a 20 wrench in it. And true to form, in the Bonney 1925 catalog their smallest wrench is the 721. However, in the Bonney 1933 catalog, their smallest wrench is a 1020 (5/16" x 1/4").
If you don't understand ISN-embedded model numbering schemes, the "20" is the ISN. The "1" is a type of wrench or steel prefix that many mfgrs, including Bonney, used to distinguish engineers wrenches of different compositions, typically alloy from carbon, or alloy from special alloy. The "0" is just a filler, because that digit is needed for ISN's with a "7" prefix. Williams' first wrenches all had whole number model numbers, 21 through 40 or whatever. When they started making them with new, different milled openings, they needed a way to give them a model number that fit the system, but all the whole numbers were taken, so they used the "7" prefix to squeeze in a smaller wrench, and a letter (A, B, and C) suffix to squeeze in larger wrenches. A 723 (3/8" x 7/16"), for example, is smaller than a 23 (13/32" x 1/2"), but they couldn't give it a "22" because that was already taken for the 5/16" x 1/2" wrench. A 723-A (3/8" x 1/2") is bigger than a 23, but they couldn't give it a "24", because that was already taken for the 13/32" x 19/32" wrench. If you look at any DOE wrench chart in any period catalog, this will all become very apparent.
That was all necessary prelude to make sure the significance of my real point is understood.
Bonney's carbon steel line wrenches had straight up ISN numbers. Their CV line used 1XXX. Later, their Zenel line used 3XXX.
A Bonney CV eng wrench with 5/16" x 1/4" openings, therefore, was model number 1020. "1" for the series, "0" as filler, and "20" as the embedded ISN.
A Bonney -ZENEL- eng wrench with 5/16" x 1/4" openings was model number 3020. "3" for the series, "0" as filler, and "20" as the embedded ISN.
To emphasize my point, here're examples that have a 7XX ISN...
A Bonney CV eng wrench with 7/16" x 3/8" openings was model number 1723. "1" for the series, and "723" as the ISN.
A Bonney -ZENEL- eng wrench with 7/16" x 3/8" openings was model number 3723. "3" for the series, and "723" as the ISN.
Finally, the point.
A Bonney carbon steel wrench with 7/16" x 3/8" openings was model number 723. No prefix for CV or Zenel. Just 723. And again if you look at any wrench charts, you will find 27's, 727's, and 727C's, 29's and 729's, etc etc.
A Bonney carbon steel wrench with 5/16" x 1/4" openings should have been a "20", NOT a "720." The "7" in "720" implies smaller than "20" sizes.
When Bonney decided to make a wrench smaller than the 721 in 1929, I think they made a mistake giving it the 720. It should've been just a 20. And it was a mistake they recognized and corrected in the 1933 catalog.
You have a cool novelty wrench there.