Leonardo da Vinci drew an early ball-bearing design as a way to reduce friction between moving surfaces.
His sketches show balls arranged so that one surface could move against another with rolling contact rather than direct sliding contact. This principle reduces friction and helps machinery move more efficiently. Leonardo studied the idea while investigating mechanical systems and the behavior of moving parts.
The drawing is important historically, but Leonardo did not invent the complete modern ball bearing used in industrial machines. His design was an early conceptual step toward rolling-element bearings, and it did not include all the features needed for a practical, durable bearing.
Modern ball bearings generally use balls held between inner and outer rings, often with a cage that keeps them spaced. They became especially important during industrialization, when machines needed reliable, low-friction rotation at higher speeds and loads.