What Leonardo da Vinci invention used rolling spheres to reduce friction?

Leonardo da Vinci designed a ball bearing using rolling spheres to reduce friction.

His sketches showed balls placed between rings so that one surface could rotate against another with less sliding resistance. Rolling contact generally produces less friction than direct sliding contact, making the arrangement useful for rotating machinery.

Leonardo studied the idea while examining mechanical systems and the behavior of friction. The drawings are often cited as an early record of a bearing concept, although modern ball bearings developed through later engineering and manufacturing advances.

The design should not be confused with a complete modern bearing assembly. Leonardo’s sketches explored the principle, while standardized sealed bearings and precision-made races appeared much later.