Here you can see the details of the trailer hitch. Incorporating the universal joint from the socket set. This gives the hitch vertical and horizontal movement but not twist (IE if one wheel goes over a bump). To allow for twist I elongated the hole where the bolt goes through holding the socket drive to the trailer. I then used a thin bolt so it was loose. To stop it all from vibrating I made up washers of old bike tube that act as a buffer.