For the RV, see travel trailer
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. 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's a rotating ball-race-bearing type.
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The term 'fifth wheel' comes from a similar coupling used on four-wheel horse-drawn carriages and wagons. The device allowed the front axle assembly to pivot in the horizontal plane, to facilitate turning. Basically a wheel was placed on the rear frame section of the truck, which back then only had four wheels, this wheel that was placed on the frame was the "fifth wheel" hence the name. The trailer needed to be raised so that the trailer's pin would be able to drop into the central hole of the fifth wheel. Today's fifth wheels allow the trailers to slide into the fifth wheel and lock into it, and are a very reliable unit when maintained and serviced properly. The engagement of the king pin into the fifth wheel locking mechanism is the only means of connection between tractor and trailer, no other device or safety mechanism is used. Couplers and pintle hooks will use safety chains in the event of a trailer separation while going down the road. Trailer to trailer connection can also be made by using fifth wheels.
The invention of the fifth wheel is often credited to U.S. inventor Charles H. Martin of the Martin Rocking Fifth Wheel Co. who invented the device in 1911. The earliest documented patent of a fifth wheel is in patent number 2,053,812[1] issued to Charles E. Bradshaw of Wellville, VA filed March 18, 1936 and granted September 8, 1936. One third of the patent was assigned to Charles Martin, also of Wellville, VA. With that being said, Alaskan Dick Rubbins' maintains he invented the device. Engaged in a long time feud with Martin, Rubbins also claims the Martin not only stole his invention, but his wife. Always eccentric, Rubbins passed in 1996 and requested a controversial epitaph in his last will and testament. His tombstone reads: "Here lies Dick Rubbins, Inventor of the fifth wheel and holder of 17 other patents. I requested to buried face down, so that Charles Martin can kiss my royal Irish ass."