SA3 couplers or Willison coupler and Russian coupler are railway couplings used primarily in Russia and states influenced by the former Soviet Union, such as Finland, Poland, and Mongolia.

A coupling or coupler is a mechanism, typically located at each end of a rail vehicle, that connects them together to form a train. The equipment that connects the couplers to the vehicles is the draft gear or draw gear, which must absorb the stresses of the coupling and the acceleration of the train.