Western Australian Current Regulations Western Australian Current Regulations (1) A fifth wheel
coupling, the mating parts of a coupling, a kingpin or a towbar must not be
used for a load more than the manufacturer’s load rating.
(2) A kingpin must be
used only with a fifth wheel coupling that has a corresponding jaw size.
(3) The mating parts
of a coupling used to connect a semi‑trailer to a towing vehicle must
not allow the semi‑trailer to roll to an extent that makes the towing
vehicle unstable.