The fifth wheel is the primary coupling mechanism between a heavy-duty truck and a semi-trailer. It consists of a large, flat steel plate with a slot that captures the trailer kingpin, locking it in place with internal jaws. This pivot point supports the front weight of the trailer while allowing the articulated vehicle to turn corners smoothly.
Heard on the job
Make sure you grease the fifth wheel before you hook up that new dry van.
Insider tip
A high hook happens when the trailer is too high and the kingpin slips over the fifth wheel instead of locking into the jaws, potentially dropping the trailer on the truck frame.
Also heard as
- fifth wheel coupling