What mechanical component did Leonardo da Vinci study using balls between rings?

Leonardo da Vinci studied a ball bearing using balls positioned between rings to reduce friction.

His notes and sketches from the late fifteenth century show a bearing arrangement in which balls could move between inner and outer surfaces. The basic aim was to prevent the two rings from rubbing directly against each other. Separating surfaces with rolling elements reduces sliding friction and allows rotary motion to continue more easily.

Leonardo is often credited with an early ball-bearing concept, not with inventing the complete standardized bearing industry. His design appears to have addressed a common problem in machines: how to support rotating shafts while limiting resistance. Modern ball bearings use carefully manufactured races, cages, lubrication, and hardened steel or ceramic balls. Those later refinements made bearings reliable in clocks, engines, vehicles, and industrial machinery, whereas Leonardo's drawings remained conceptual or experimental designs.