Leonardo da Vinci drew an early ball-bearing concept using spheres between moving surfaces.
A ball bearing reduces friction by replacing sliding contact with rolling contact. In Leonardo’s sketches, balls are positioned so that an inner and outer part can move relative to one another while the spheres carry the load. He also considered ways to keep the balls separated, an important practical issue because touching balls would increase friction and cause wear.
The concept appeared in Leonardo’s studies of mechanical motion around the late 15th century. It was not the same as a modern standardized bearing, which uses precisely manufactured races, cages, seals, and hardened materials. Leonardo’s drawing is best understood as an early conceptual step toward rolling-element bearings.
Ball bearings later became essential in clocks, machines, bicycles, vehicles, and industrial equipment. Leonardo’s sketch is often cited as evidence of his ability to connect abstract mechanical principles with practical machine design.