This is purely a guess based on the following information:
Are you talking about part #20 in the pic? Parts tree says there is a nyloc nut that goes with it. That nyloc nut crosses (per parts tree) to a 3/4-16 nyloc nut for a 44a mower deck spindle. A 3/4" nut takes a 1-1/8" wrench.
image.jpg
http://www.partstree.com/parts/cub-c...sion-controls/
Bill