What machine component did Leonardo da Vinci study using a ball-and-ring design?

Leonardo da Vinci studied a ball bearing using a ball-and-ring design.

His sketches show balls placed between surfaces so that one part could rotate with less sliding friction against another. The basic principle is that rolling contact generally creates less friction than direct sliding contact. Leonardo was investigating this arrangement while studying machines and mechanisms in the late 15th century.

Leonardo did not invent the modern standardized ball bearing, which depends on carefully manufactured races, cages, lubrication, and precise tolerances. His drawings are significant because they show an early understanding of the value of rolling elements. The concept later became essential in machinery, clocks, bicycles, engines, turbines, and many other devices.