Leonardo da Vinci drew a ball bearing as a set of balls intended to reduce friction between moving parts.
In a bearing, rolling elements separate two surfaces so that one can move with less sliding friction against the other. Leonardo’s notebooks include a design using balls in a ring, an arrangement recognizable as an early ball-bearing concept.
The drawing is significant because it addresses a real mechanical problem: if balls touch one another or become crowded, they can hinder smooth motion. Leonardo’s design included a separator-like arrangement to keep the rolling elements apart, anticipating an important feature of later bearings.
Leonardo did not invent the complete modern bearing industry, and his sketch was not the same as a factory-produced sealed bearing. It is better described as an early design or concept that resembles the principle used in modern ball bearings.