A lot of people have asked me about the hitch that I use on my now 11 year old home-built bicycle trailer. So I have recently taken a few photos of it for you all.
A brief recap:

The trailer just after I had refurbished it about 18 months ago:



and recently ready for action on a charity shop run:



The components laid out before final fitting on to my bicycle's frame. I use a spring loaded quick attach 10 mm industrial ball joint assembly for the actual hitch; these are often found on the connecting rods of process machinery. I made up a suitable fixing arm for the ball joint from a length of 16 mm diameter steel bar, mitred it, welded it to a piece of 4 mm thick mild steel plate, and for the fitting I utilised 3 of 8 mm X 40 mm diameter stainless steel socket head bolts, 5 Stainless Steel flat washers, and 2 stainless steel nylock nuts; the lower bolt is threaded into the bottom of the 16 mm steel bar:



Fitted into position:



Note; that it has left sufficient room to accommodate my bike lock under the saddle:



and finally with the trailer hitched up and ready for a utility run:



Note; the piece of chain and the padlock that I have included. This gives me some additional security when the bike and trailer are left outside of a shop, or parked up at the city cycle stands, and also as an extra safety device for if the trailer should ever jump the hitch when I am towing a load, etc.