Sure looks like an Eberhard manufactured wrench for an O. K. Champion potato digger.
Now I wonder if there is a full set.
According to Rathbone the company was started by "OK" Otto Knoerzer as the Champion Potato Machinery Co, and is now The Champion Corporation.
There are only five known OK Champion wrenches. Two are double open ended s-wrenches like yours (Nos 59 and 69).
Without Eberhard's "E" in a circle logo couldn't definitely say they were made by Eberhard. John Pope's patent that was assigned to Eberhard is a little different. As a side note this was one of thirty consecutive design patents issued to Pope on the same day.
http://www.datamp.org/patents/advance.php?pn=D13434&id=15784&set=5 (http://www.datamp.org/patents/advance.php?pn=D13434&id=15784&set=5)
(http://www.datamp.org/images/15784-1.jpg)
(http://www.datamp.org/images/15784-2.jpg)