[Womble]

Yup, Stufe and Bloomer are right - that's a standard ball hitch that's designed to bolt to a steel box-section drawbar on the trailer (i.e. a trailer without any hitch on it currently). It's not actually designed to fit onto a trailer that already has a ring for a pin hitch. However, as already said, you could probably line up one hole with the ring on your existing trailer and bolt through, then perhaps drill another hole a bit further back to suit the second hole on the ball hitch for a second bolt. It's hard to tell without seeing what your existing pin hitch looks like, but for use with a wee trailer around the farm, I'm sure you'll be able to work something out.

[Le Recoignot]

try the 'Towsure' website, they usually have that sort of gear at reasonable prices.