What object did Leonardo da Vinci sketch as an early form of a ball bearing?

Leonardo da Vinci sketched an early form of a ball bearing.

Leonardo’s notebooks contain drawings of balls placed between rings so that one surface could move against another with less friction. These sketches are commonly cited as an early ball-bearing concept. The balls were intended to separate moving surfaces, reducing rubbing contact and making rotation easier.

The idea was part of Leonardo’s broader mechanical studies. He investigated gears, axles, screws, friction, and transmission systems while designing machines for workshops, military engineering, and theatrical effects. His drawings show that he understood the practical value of rolling motion compared with sliding motion.

Leonardo did not create the standardized precision bearings used in modern machines. His sketches lacked the manufacturing methods and hardened materials needed for reliable mass production. Modern ball bearings use carefully shaped balls, races, cages, lubrication, and close tolerances. The historical claim is therefore about an early recorded design, not the invention of the complete industrial bearing system.