The
fifth-wheel coupling provides the link between a
semi-trailer and the towing
truck,
tractor unit,
leading trailer or
dolly. Some
camper trailers use a fifth-wheel configuration, requiring the
coupling to be installed in the bed of a
pickup truck as a towing vehicle, and "fifth wheel" is therefore sometimes used as a synonym for such campers in North America. The coupling consists of a
kingpin, a diameter steel pin 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 (with the kingpin at the center) rotates against the surface of the fixed fifth wheel, which does not rotate. To reduce friction, grease is applied to the surface of the fifth wheel. The configuration is sometimes called a
turn-table in
Australia and
New Zealand, especially if it is a rotating
ball-race-bearing type. The advantage of this coupling is improved towing stability.