The one I have on my bushtec is a pin on the hitch and a rotating knuckle coupler, kind of like a tie rod end. The coupler for the trailer spins 360 degrees and the horizontal play is about 45 each way. There is a picture of the trailer coupler here under chrome chassis neck . .
Bushtec Full Line Accessories
If you are using a ball type hitch, the coupler still spins 360 degrees but you only have about 30 degrees of horizontal play.
Think of the horizontal the same as on a car but the main shaft from bike to trailer in two pieces that rotate 360.