SA3 coupler

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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.^[1]

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. Conversion to Janney couplers (as Japan and Australia had) was considered, as was development of a new design. The Willison coupler was patented in Germany (1914) and in US (1916) by English locksmith John Willison from Derby, England. The Knorr-Bremse company bought the invention in 1912 and it started to be used in Germany for some heavy trains and some suburban trains in Berlin and Paris. In the 1930s, the Soviets improved on this design and then decided to make this coupler standard across the Russian railway system.