<P> 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 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 . </P> <Ul> <Li> Fontaine Fifth Wheel </Li> <Li> SAF - Holland </Li> <Li> Jost GB Limited </Li> <Li> Fruehauf Automatic Semi-Coupling </Li> <Li> Capus UK Limited </Li> <Li> Eidal </Li> <Li> Tulga Fifth Wheel Co . </Li> </Ul> <Li> Fontaine Fifth Wheel </Li> <Li> SAF - Holland </Li>

Where does the term 5th wheel come from