Which part of the kingpin should the locking jaws close around?

Answer: A — The shank

The locking jaws of a fifth wheel should close around the shank of the kingpin. The shank is the part of the kingpin that extends downward and is essential for ensuring a secure connection between the trailer and the towing vehicle. When the locking jaws grasp the shank properly, they lock the kingpin in place, which stabilizes the trailer while it is being towed. This secure connection is crucial for safe operation, helping prevent unintentional disengagement between the trailer and the tractor. The other components of the kingpin—such as the base, neck, and head—serve different purposes and are not designed to be the point of connection for the locking mechanism. Therefore, ensuring that the locking jaws engage the shank correctly is vital for safe trailer operation.