Unusual coupling

This is the coupling on our semi-trailer bus. Unusual?

I have seen one before and was told it was used for trailers that wouldn't be uncoupled in normal service. Maybe someone can confirm whether what I was told was correct

Looks like a Bartlett Ball coupling. Is there a thread in the hole at the top?

There is one like that on that nice fargo truck/5th wheeler that was in vintage trucks awhile back.

Looks like a fabricated turn table Rod.
The Ball looks a lot larger than a Bartlett, they are 127 or 95 MM
Looks like you could put a Bartlett ball in the centre though if you can make the hood fit on the trailer, then you wouldn't need the ring.
Most of the fabricated greasy plate turn tables I have seen have a bit of pipe inside another piece in the centre and then a bolt through to hold it all together.

I presume the upper cup is still on the trailer. Could not bend down far enough to look.

That looks like a mill ball.

what type of truck is it on? I am thinking it may be a Crain mount. I use to drive a ww2 4x4 blitz with a crain on it that had its own wheels and would swing all the way around. cam

A 1942 Ford semi trailer

HEY Charger!! .. the turntable is a bit of a curly one, but can we have a little peek at the rest of her?....emntk .....cheers and good luck with her...