Leonardo da Vinci sketched an early ball bearing using freely moving balls.
His design placed balls between moving surfaces so they could roll instead of slide. This reduces friction and allows one part to rotate more easily in relation to another.
The drawing appears in Leonardo’s mechanical studies from around 1498. He recognized that the balls needed room to move and experimented with arrangements that prevented them from simply bunching together.
Leonardo did not create the standardized, sealed ball bearings used in modern machines. Industrial manufacturing, accurate tolerances, cages, and improved materials were developed much later. His design is nevertheless an important early example of the principle behind rolling-element bearings.