The kingpin is a solid, hardened steel pin mounted underneath the front of an HGV trailer, fixed centrally within the bed plate (rubbing plate). It is a critical component in the coupling system, as it inserts into the tractor unit’s fifth wheel and locks in place to secure the trailer.
Kingpins are precisely engineered to meet specific diameters (typically 2" or 3.5") and conform to international standards such as ISO 337. They must endure extreme vertical and lateral loads during transport, braking, and cornering.
As the primary link between the tractor and trailer, the kingpin enables safe articulation while also transferring trailer weight onto the tractor’s rear axles.
