Leonardo da Vinci sketched a ball bearing using balls between two surfaces to reduce friction.
His drawings from around 1498 show a mechanism in which metal balls could roll between rings or supporting surfaces. Instead of allowing one surface to slide directly against another, the balls changed much of that sliding friction into rolling friction. This principle is central to many bearings used in machines today.
Leonardo’s sketch is frequently credited as an early ball-bearing concept, but it was not a complete modern bearing ready for industrial production. His design also raised a practical problem: without a cage, the balls could crowd together and stop moving efficiently. Later engineers developed cages and precision manufacturing methods that made ball bearings reliable in clocks, vehicles, motors, and other machines.