What type of bearing did Leonardo da Vinci sketch to reduce friction?

Leonardo da Vinci sketched a ball bearing to reduce friction between moving surfaces.

His late-15th-century studies included balls arranged so that they would roll rather than slide against one another. This principle reduces friction and makes rotary motion more efficient. Leonardo’s sketches are among the earliest known designs showing the basic idea of a modern ball bearing.

Leonardo did not invent every later feature of industrial bearings. Modern bearings use carefully manufactured races, cages, lubricants, and materials that were developed much later. His drawings nevertheless show a clear understanding of how rolling contact could improve machines by reducing resistance.