Definition:
A rotary coupler is a conventional railroad knuckle coupler that can rotate 360 degrees in its pocket. This allows the car to stay coupled to its neighbor while being turned upside down in a rotary dumper.
Only one rotary coupler is needed for this operation. Typically, cars with this device will have a colored stripe or panel painted on the end of the car so equipped. Sometimes a car will be equipped with rotary couplers at each end to allow more flexibility for coupling locomotives to either end of the train. Solid, or unit trains of coal cars have become trademarks of American railroads for more than 20 years. Rotary couplers allow these trains to stay together from mine to consumer and back again.
