What rotating mechanical element did Leonardo da Vinci study to reduce friction?

Leonardo da Vinci studied a ball bearing to reduce friction between moving surfaces.

His notebooks contain a sketch of a bearing using balls arranged inside a ring. The balls were intended to keep the two rings apart while allowing rotation, replacing sliding contact with rolling contact. This arrangement reduces friction and can help machinery turn more efficiently.

Leonardo's drawing dates from the late fifteenth or early sixteenth century and is often cited as an early ball-bearing concept. It was not a modern standardized bearing: the design had practical limitations, including the tendency of balls to bunch together. Later bearing designs added cages or separators to keep the rolling elements spaced evenly.

The basic idea remains central to bicycles, motors, fans, machine tools, and many other devices. A ball bearing is distinct from a roller bearing, which uses cylindrical or tapered rollers instead of spherical balls.