Leonardo da Vinci drew a ball bearing using two concentric rings separated by balls to reduce friction.
The design appears in his mechanical studies and is commonly cited as an early ball-bearing concept. The balls allow one ring to move relative to the other while replacing much of the sliding friction with rolling friction.
Leonardo was not the first person to use rolling elements in machinery, and his drawing did not create the modern standardized bearing industry. Nevertheless, the arrangement shows that he understood a key principle used in later bearings for wheels, machines, and rotating shafts.
Modern ball bearings require precise manufacture, hardened materials, cages, lubrication, and controlled clearances. Leonardo's historical sketch is therefore best described as an early design or conceptual precursor, rather than a modern industrial bearing made to current engineering standards.