Leonardo da Vinci designed a ball bearing using rolling spheres to reduce friction between moving surfaces.
His bearing sketch dates from the late 15th century and shows balls arranged so that an inner ring could move relative to an outer ring. Because rolling friction is generally lower than sliding friction, the arrangement could make rotation smoother and reduce wear.
Leonardo’s drawing is an early known concept for a ball bearing, but it was not the same as a modern manufactured bearing. His sketch does not fully solve the problem of keeping the balls separated, a feature later bearing designs addressed with cages and more precise materials.
The idea belongs to Leonardo’s broader mechanical studies. He investigated gears, shafts, screws, pulleys, and other devices, often combining observations from engineering with his interest in anatomy and natural motion.