What is the upper fifth wheel?
a.The part mounted on the tractor frame
b.The flat plate and kingpin assembly on the underside of the trailer front
c.The release handle on the fifth wheel
d.The locking jaw mechanism
Explanation
The upper fifth wheel, also called the upper coupler, is the flat plate on the underside of the front of the trailer that includes the kingpin. It sits on top of the lower fifth wheel which is mounted on the tractor.