SA3 coupler
SA3 couplers (also known as СА3 or СА-3 couplers per the typical foundry stamp on top of these couplers, meaning "Советская Автосцепка, 3" in Russian or "Soviet Auto-latch 3" in English) 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. Russian railways originally used buffers and chain couplers during Imperial era, however these had several disadvantages: their draft load was limited, they were susceptible to buffer lock, and they were not semiautomatic like the North American Janney couplers.