Stoney,
Here's an excerpt from a Whitman & Barnes Lawnmower Parts Book that shows a No. 123 wrench shaped like your wrench. I have this wrench marked with the 1232 number and unmarked like yours. The unmarked ones are found with flat sides like yours and with raised outer edges. I will get a picture posted later.
(http://i222.photobucket.com/albums/dd3/buswrench/message-board/WB-lawnmower-wrenches.jpg)
Here's a pic of my variations:
Top - Raised edges with P123 part number.
Center - Raised edges, no markings.
Bottom - Flat sides, no markings (like Stoney's).
They are all the shape and same opening sizes.
The parts List states the P123 was used only during 1904.
(http://i222.photobucket.com/albums/dd3/buswrench/message-board/P123-WB-lawnmower-wrenches.jpg)