Leonardo da Vinci studied a ball bearing as an early solution for reducing friction between moving parts.
In his Codex Madrid I, Leonardo drew bearing arrangements using balls placed between rings or races. The balls were intended to roll rather than slide, allowing one component to turn more freely against another. This principle remains central to modern rolling-element bearings.
Leonardo was not the first person to use rolling objects in machines, and his sketches were not a complete standardized manufacturing system. His importance lies in recognizing how separated rolling elements could prevent direct rubbing between surfaces. He also considered ways to keep the balls apart, because clustered balls can create resistance and uneven motion.
The word “bearing” covers many designs, including plain bearings, roller bearings, and ball bearings. Leonardo’s relevant sketches specifically involve balls, so ball bearing is the most precise answer. Industrial ball bearings became practical much later, after advances in steelmaking, precision machining, and mass production.