Steel Soldiers now has a few new forums, read more about it at: New Munitions Forums!
Go buy a 3/8" all-thread coupler. Or just jamb 2 nuts together on a 3/8-2" long bolt, and use a wrench on it.
Coupling Nuts | Fastenal
9/16" is correct....... What size hex-head is needed for the deuce winch drain plugs?.....