Many a HGV trailer has been given a second lease of life on farm work, and, while some are modified with a conventional drawbar, it’s also commonplace for a dolly with its fifth wheel coupling to be installed. We run through how this hitch system works

The pivot point between truck and trailer is the kingpin. Mounted on the trailer this pin is designed to engage with the coupling mechanism of the fifth wheel. The pin’s vertical notch or groove meshes with the coupler to secure it.