Leonardo da Vinci sketched a ball bearing to reduce friction between moving parts.
His drawings show balls arranged between surfaces so that motion would involve rolling rather than direct sliding. This arrangement reduces friction and can help support a rotating shaft or moving mechanism.
Leonardo studied bearings while examining machines, gears, mills, and other mechanical systems. His sketches are often cited as an early documented treatment of the ball-bearing principle, although similar rolling-element ideas appeared in earlier engineering traditions.
Leonardo did not create the modern standardized bearing industry. Contemporary ball bearings use carefully manufactured races, cages, and hardened balls. The historical importance of his drawings lies in clearly applying rolling elements to mechanical design.