Coupler

The coupler is the assembly at the front of a trailer tongue that drops over the hitch ball and latches. Together with the ball it forms the articulated joint that allows turning and pitching while keeping the trailer attached.

Coupler size must match the ball diameter (1⅞″, 2″, 2⁵⁄₁₆″). Always insert a pin or locking clip after latching. A worn coupler is a frequent cause of trailer separation — replace if play exceeds ~3 mm or visible corrosion appears. Not to be confused with a fifth-wheel kingpin, which uses a saddle-style hitch instead of a ball.