Leonardo da Vinci drew a ball bearing that used metal balls between rings to reduce friction.
His late-15th-century sketches show balls arranged so that one ring could move relative to another while the balls rolled between them. This arrangement addressed a basic mechanical problem: sliding contact creates more friction than rolling contact. Separators were also included in some drawings to keep the balls from crowding together.
Leonardo’s design is often called an early ball-bearing concept, but historians should distinguish a drawing from a manufactured, standardized bearing. Industrial production of reliable bearings required later advances in metallurgy, machining, lubrication, and manufacturing precision.
A ball bearing is also different from a roller bearing. Ball bearings use spherical rolling elements, whereas roller bearings use cylindrical or tapered rollers. Both belong to the wider family of rolling-element bearings and are used to support rotating shafts while limiting friction.