Vintage trailer hitch?

[hair bear]

Question for you...
In the early 1980s the farmer I worked for had a late 50's lwb series 1 landrover. The tow hitch on it I'd never seen before or since. It consisted of a 2 bolt casting that fitted to the truck the same as an iso ball hitch, but the casting had a vertical hole/sleeve about 1 1/2" diameter about 2" long with a sort of spring clip arrangement on the bottom. The Rice style trailer had a hitch with a corresponding downward facing pin that had a groove in it which the clip mechanism locked into, and was part on the normal overrun brake system.
It was a complete manufactured hitch system, and definitely not home made.
Any ideas?

[Jeremy Rowland]

Having a quick look, I came across two different types of hitch, one referred to as a NATO hitch and the other in the picture below.

Jeremy

[hair bear]

Ok, so if you could imagine that as a solid casting (no jaw opening) with the pin hole drilled through from top to bottom, and the pin itself as fixed part of the trailer head, it would drop in from the top and clip at the bottom.