Any of these tools should work:
-Great Neck CO8C 15/16''Comb.Wrench Carded
or
TEKTON 14251 1/2-Inch Drive by 15/16-Inch Deep Socket, 6-Point
or
Wilmar 3/8" Drive, 15/16" Socket (W38030)
I did not test it with those myself, so buy at your own risk. If you don't have a big enough socket wrench to handle the sockets, you are better off buying the combo wrench. You may still need to use a piece of pipe as a breaker bar to loosen the center nut on the blades of the mower deck.
For search engines:
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For those with an impact driver, this should work for you: