(The equipment on the cab unit used to hold the kingpin on a semi-trailer)
Photo courtesy of Travelaire A trailer and hitch configuration connected to the tow truck directly above the rear axle by way of a special fifth wheel hitch. This causes several feet of the connected trailer to hang over the tow truck, placing about 15 to 25% of the trailer's weight on the rear axle of the truck. Commercial trucks and trailers use this hitch configuration. Also commonly spelled as 5th wheel. For additional details see Fifth Wheel - An Introduction.
The sloping plate with two hinged jaws, which is fitted to the back of the tractor unit of an articulated vehicle and receives the pin on the front of the trailer portion.