Fifth-wheel coupling

>>The fifth wheel coupling provides the link between a semi-trailer and the towing truck, tractor unit, leading trailer or dolly. Some recreational vehicles use a fifth wheel configuration, requiring the coupling to be installed in the bed of a pickup truck as a towing vehicle.

>>The coupling consists of a coupling pin (or kingpin) on the front of the semi-trailer, and a horseshoe-shaped coupling device called a fifth wheel on the rear of the towing vehicle. The surface of the semi-trailer rotates against the surface of the fixed fifth wheel, which does not rotate.