What device did Leonardo da Vinci design to demonstrate the principle of a ball bearing?

Leonardo da Vinci designed a ball-bearing mechanism to demonstrate rolling motion between moving surfaces.

Leonardo’s Codex Atlanticus includes a sketch of a device using balls placed between rings. The arrangement allowed the rings to move with less sliding friction, illustrating the basic principle behind a ball bearing. The balls were not intended to carry a modern machine shaft in the fully engineered sense, but the drawing shows Leonardo’s clear understanding of the advantage of rolling contact.

The concept is often linked to Leonardo’s studies of friction and mechanical motion during the late fifteenth century. He explored how surfaces resist movement and how machines could be made more efficient. His bearing design included separators intended to prevent the balls from touching one another, an important feature in later bearing technology.

Leonardo did not invent every form of bearing. Ancient and medieval machines used rollers and other low-friction devices. His importance here is that he recorded a recognizable ball-bearing arrangement centuries before industrial bearings became common.