Coupler Gauging: Coupler Contour

Coupler contour gauging is the inspection of the working contour of a coupler - the curved mating surfaces of the knuckle and coupler head that interlock when two cars couple together - for wear against the standard coupler contour. Because every interchange coupler must mate with every other one, the contour is held to a common standard.

Why It Matters

As couplers carry slack action and buff and draft forces in service, the knuckle and contour faces wear. A worn contour lets coupled cars sit looser together and, past the limit, can let the couplers work apart or fail under load - a coupler separation that drops cars or breaks a train in two. This vertical-separation risk is greatest with E couplers; F couplers carry interlocking top and bottom shelves designed to resist a coupler riding apart, but their contour faces still wear and are gauged the same way. Gauging the contour catches this wear before it becomes a parting hazard.

Procedure

The inspector applies an AAR coupler contour gauge to the coupler. The gauge is shaped to the contour limits; if the worn coupler still fits within the gauge it passes, and if the contour has worn beyond the gauge's limit the coupler is condemned and replaced. Separate gauges apply to the two common coupler types - the **E coupler contour** and the **F coupler contour** - so the correct gauge for the coupler type is used. The governing contour limits are defined in the AAR interchange rules and field manual.