Tightlock coupling

They have mechanical features that reduce slack in normal operation and prevent telescoping in derailments, yet remain compatible with other Janney types used by North American freight railroads.

Type H couplers are in widespread use on multiple unit passenger trains in the UK built from the mid 1970s onwards.

In order to reduce staffing costs and cut down station dwell times, British Rail looked to incorporate an automatic coupler mechanism in its new power-door trains.

Air-operated Tightlock couplers were chosen, together with underslung electrical connector boxes controlled by a Drum switch, and this allowed drivers to single-handedly attach or split a train without having to leave the cab.

The constant couple-uncouple cycles of heavy London commuter services caused the couplers' mechanisms to wear out faster than expected.