fifth wheel
mechanics
Quick Summary
A fifth wheel is a mechanical device used to connect a truck tractor to a semitrailer, allowing for articulation between the two units. It typically consists of a lower half mounted on the truck tractor and a kingpin on the semitrailer that connects to it. This coupling mechanism is designed to support a portion of the semitrailer's weight and load. The term "fifth wheel" can also refer to a similar support on a carriage to prevent tipping, or more figuratively, to someone or something that is superfluous or unnecessary.12
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