A self-discharging car (860630) is equipped with a mechanism—typically bottom hoppers, rotary couplers, or conveyor systems—that allows it to unload its cargo without manual intervention. An open car with fixed high sides (860692) has no such mechanism and must be unloaded by external equipment such as a crane or rotary dumper acting on the car itself. The presence or absence of an integral discharge mechanism is the classification criterion.

Intermodal well cars and flatcars designed to carry shipping containers are generally classified under 8606 as freight cars (typically under 860699 as NESOI freight cars), since they are non-self-propelled railway vehicles designed for freight carriage. The containers themselves, if imported separately, classify under heading 8609.