I would assume that wrench came with an old walking push type cultivator, yes, the center is for wing nuts, the other two openings
would most likely be used to assemble the handles upon receiving them in the mail, plus putting on and removal of accessories that
would come with the unit, like cultivators, soil/plows, weeder, and other types of implements used in the home gardens.
it's too late, cold & snowy to go out and look for mine.