Leonardo da Vinci sketched a ball bearing as a way to reduce friction between moving parts.
His drawings from the late fifteenth century show balls arranged so that surfaces could move with rolling contact rather than sliding contact. Rolling generally reduces friction and wear, which is useful in machines that rotate around an axis. Leonardo’s arrangement is often cited as an early ball-bearing concept.
The sketch was not the same as a fully standardized modern bearing. Contemporary bearings use carefully manufactured races, cages, precise clearances, and hardened materials. Leonardo’s design appears to have been intended to prevent the balls from rubbing against one another, an issue that later bearing designs had to solve.
Leonardo is sometimes credited with inventing the ball bearing outright, but the safest description is that he documented an early design. Related rolling-element ideas existed in other forms, and industrial bearing manufacture developed much later. His drawing nevertheless demonstrates his understanding that rolling contact could make complex machines more efficient.