[thackney]

I have an oddball trailer. custom built with 3 axles. It uses a plain old bumper hitch but with a large ball size.

You have another problem. Ball hitches are not constructed to meet this large of a towing capacity.

http://hitches4less.com/trailer-hitch-classes.html

http://www.sizes.com/home/trailer_hitches.htm

[mamelukesabre]

hitch balls go up to 3 inches and larger.

[mamelukesabre]

and I make my own hitch receivers out of 3/4” plate.