In Australia, we call this a "Tregg Hitch, a simple pivoting poly block with a shaft through tubing mounted on a steel plate takes the place of the trailer hitch.That is a good looking trailer you have there. Built mine to be a meat trailer for hunting in the rough going here in Alaska. My hunting partner built mine 10 years ago and have hauled out many moose and caribou with it so far. No trails where we go with muskeg,rivers and tussocks to tackle so we don't like the idea of an axle to hang up on the underneath.
2 foot of ground clearance to keep the load high and dry with a working tailgate and big enough for me to sleep in and stay off the cold ground in a pinch. Coolest thing about it is his just patented swivel hitch that rotates 360 degrees with crazy angles so if you flip the machine or trailer it doesnt take the other with it or worse yet snap a ball and leave ya stranded.
Id show pics of the hitch itself but he's still hush hushing it trying to work a few deals with a couple companies. It pulls behind the Foreman quite nicely....
The receiver pin goes through a hole in the centre of the poly block which has a steel bush lining it for extra strength.
My brother is a boiler maker (Welder) he has manufactured smaller versions for his lawn tractor trailer and tow behind implements out of stainless steel including the block.
They are a must on any towable vehicle going off-road in Australia, normal hitches just don't cut it where these things practically never fail.