Leonardo da Vinci sketched a ball bearing to reduce friction between moving parts.
His drawings from the late 15th century show small balls arranged so that one surface could move over another with less sliding friction. The concept is associated with Leonardo’s studies of machines and appears among designs connected with the Codex Atlanticus.
A ball bearing works because rolling contact generally creates less resistance than sliding contact. The balls are normally held between inner and outer rings, although Leonardo’s early concept did not necessarily include the complete cage and raceway arrangement used in modern bearings.
Leonardo was not the first person in history to use rolling elements, and his sketch did not create the modern bearing industry. Ancient machines used rollers in various forms. His importance is that he documented a compact, recognizable ball-bearing concept during the Renaissance.