coupling pin

plural coupling pins

1. Any pin used to form a connection between two mechanical or structural components.
   1. A pin used to connect train cars or a trailer to a towing vehicle.

      He would tell them about the cablegram when they were all on board the train. Then he ran out upon the platform just as the engine whistled twice in the final warning that precedes the first rumbling jerk of coupling pins.

      1913, Edgar Rice Burroughs, The Return of Tarzan, New York: Ballantine Books, published 1963, page 98

   2. A pin for joining scaffolding frames or pipes.