What rotating mechanism did Leonardo da Vinci sketch as an early ball bearing?

Leonardo da Vinci sketched a ball bearing mechanism using rolling balls to reduce friction between moving surfaces.

The drawing appears in Leonardo’s studies of mechanical systems from the late 15th or early 16th century. It shows balls arranged in a ring so that parts could rotate while the balls separated the moving surfaces. This arrangement reflects the central principle of a modern ball bearing: rolling contact generally creates less friction than sliding contact.

Leonardo did not invent the complete modern bearing industry, and his sketch was not a standardized, sealed component. The design also raises practical issues such as keeping the balls evenly spaced and preventing them from rubbing together. Later engineers developed cages, hardened materials, accurate machining, and lubrication.

A ball bearing differs from a roller bearing, which uses cylindrical or tapered rollers. Leonardo’s concept is historically important because it clearly anticipates the use of balls in a rotary bearing, even though industrial production came much later.