Leonardo da Vinci sketched a ball bearing using balls between moving surfaces to reduce friction.
His notes and drawings from around 1498 show an arrangement in which rolling balls separate two rings. This allows one part to rotate more easily against another because rolling friction is generally lower than sliding friction. Leonardo also considered ways to keep the balls from crowding together.
The idea was not an invention of the modern industrial ball bearing in its complete form. Similar rolling elements had been used earlier, and later engineers developed more durable materials, cages, lubrication systems, and manufacturing methods. Leonardo’s contribution was a clear early study of the principle and its mechanical applications.
The sketch is sometimes linked to his work on reducing friction in machines, but it should not be confused with a finished bearing produced in Renaissance workshops.