Ben,
Here see if this helps. Used a little pic editing to help show the point.
Posted edited 1-15-12 to better reflect what is going on at the ball coupler. Incorrect pictures removed. See page 4. The tapered shank tow ball. No nut, just a through pin on the bottom.
And the turning radius before the chain plate hits the shank. Looks like it might be 45 degree unless this is an optical illusion.
OK, now how do you get the top ball sphere pushing back into the latch mechanism when WD is applied?
What am I missing?
OK I found what I was missing...LOL see page 4John