CA-3 Automatic Coupler Head SA-3 Hook Buffer for Russian Freight Cars CA-3 / SA-3 coupler is the main coupler for former Soviet Union Railways. It has a higher impact speed and provides significant traction effect under extreme climate conditions. It is classified as a non-rigid automatic coupler and can tow goods with a total weight of more than 8000 tons under bad weather conditions. The CA-3 coupler head is composed of the coupler body, coupler lock, lock pawl, lock stop,