What machine did Leonardo da Vinci design to make large metal balls easier to move?

Leonardo da Vinci designed a ball-bearing mechanism to reduce friction between moving surfaces.

His sketches show balls arranged so that one moving component could roll against another instead of sliding directly across it. Rolling contact generally produces less friction than sliding contact, making heavy rotating or moving parts easier to operate.

The drawings are associated with Leonardo's studies of mechanics and machines. They are important because they show a clear early understanding of the usefulness of rolling elements. However, Leonardo did not create the standardized, enclosed ball bearings used in modern machinery.

The invention is sometimes described as the modern ball bearing itself, but that is too broad. Later engineers developed manufacturing methods, cages, races, lubrication systems, and standardized sizes. Leonardo's contribution is best described as an early ball-bearing concept or rolling-element mechanism.