: This often refers to the K80 ball hitch, which allows for higher vertical loads (up to 4 tons) and better maneuverability compared to traditional bolt hitches.

A more literal "ball train" was an experimental Soviet project in the 1930s designed by Nikolai Yarmolchuk.

: Instead of traditional wheels, the train cars sat on massive motorized spheres that ran in a semi-circular concrete trough.