What type of bearing did Leonardo da Vinci study using rolling balls?

Leonardo da Vinci studied a ball bearing using rolling balls to reduce friction.

His mechanical notes include designs in which balls are placed between moving surfaces. The balls roll rather than allowing one surface to slide directly against another, reducing friction and helping rotary parts move more freely. Leonardo also considered ways to keep the balls separated so they would not bunch together.

This principle is central to modern ball bearings, although Leonardo’s designs were not identical to standardized industrial bearings. His sketches are often cited as an early study of the rolling-element bearing concept. The idea was valuable for machines with shafts, wheels, and rotating assemblies.

A ball bearing is different from a sleeve bearing, where a shaft slides inside a lubricated surface. It is also different from a roller bearing, which uses cylindrical rollers instead of spheres. Leonardo’s proposal is notable for applying rolling balls to mechanical friction control.