Leonardo da Vinci designed an early ball bearing to reduce friction between moving parts.
Around 1498, he sketched balls placed between rings so that one surface could rotate against another with less sliding friction. The balls roll, rather than allowing the surfaces to rub directly across each other, which makes rotary motion more efficient.
Leonardo’s study formed part of his mechanical investigations into motion, machines, and friction. His drawings show the principle clearly, but they do not establish that he produced a practical, standardized bearing like those manufactured today.
The idea is sometimes credited to Leonardo as the inventor of the modern ball bearing. A more precise description is that he made an important early drawing of the principle. Modern bearings use carefully manufactured races, cages, seals, and precisely sized balls.