The Rolex mechanism patented in 1931 that enabled automatic winding through a freely rotating rotor was the Perpetual rotor.
Rolex developed a self-winding system based on a rotor that could rotate through 360 degrees as the wearer moved. The company patented the design in 1931, and it became central to Rolex’s automatic movements. Unlike earlier bumper systems, which moved through a limited arc and struck stops, the freely rotating rotor could wind the watch in both directions of its motion.
The term Perpetual is often confused with the Oyster case. Oyster refers to Rolex’s water-resistant case concept, introduced in 1926, while Perpetual refers to the automatic winding system. Rolex later used both ideas together in many watches, helping create the familiar Oyster Perpetual designation.