What Leonardo da Vinci design is commonly credited as an early ball bearing?

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

His drawings from around 1498 show balls placed inside a ring or raceway. Because the balls roll rather than allowing two surfaces to slide directly against each other, the arrangement illustrates the basic principle of a modern rolling-element bearing.

The design is commonly described as an early ball bearing, although it was not necessarily a complete, sealed bearing suitable for industrial use. Leonardo’s sketch shows the mechanical idea clearly, but surviving evidence does not establish widespread manufacture or practical deployment of the device.

The concept should not be confused with the ball-bearing systems used in modern engines and machinery. Those later bearings benefited from improved materials, precise manufacturing, lubrication, and protective housings. Leonardo’s contribution was a clear Renaissance-era study of rolling friction.