Leonardo da Vinci used wooden balls in an early ball-bearing design.
Around 1498, Leonardo studied ways to reduce friction between moving surfaces and drew a device containing balls that could roll freely. The wooden balls separated the moving parts so they would not rub directly against one another. This is the basic principle behind a ball bearing: rolling contact generally creates less friction than sliding contact.
Leonardo’s drawing is often credited as an early ball-bearing concept, but it was not a complete modern bearing assembly. His design reportedly included features intended to stop the balls from touching one another, showing that he understood a practical problem in bearing operation. Modern bearings normally use hardened steel or ceramic elements, cages, races, lubrication, and carefully controlled tolerances. Leonardo’s contribution was a mechanical study and design concept, not the invention of the industrial bearing as manufactured today.