English to French Tech/Engineering Mechanics / Mech Engineering Engins de chantier

Extrait du manuel d'installation, d'utilisation et de maintenance d'une cisaille à ferraille qui se monte sur un engin de chantier :

WHAT IS FIFTH-WHEEL COUPLING USED FOR
The fifth-wheel coupling is the element allowing the rotation.
It is composed by two concentric rings.
These two rings are connected to each other by steel spheres, preventing that one ring leave the other.
The two rings can only rotate to each other on the same axis.
The internal ring has a steel toothed crown gearing with the pinion of the gear motor.
The fifth-wheel coupling is fixed between the equipment and the rotation group by bolts.
These bolts have a fundamental importance and must be controlled with the utmost care.

Quelle est la traduction de fifth-wheel coupling dans ce contexte ?
Le ERNST indique "sellette d'accouplement articulée", mais ce terme concerne l'attelage, les remorques...

Merci pour votre aide !