What early machine part is Leonardo da Vinci often credited with sketching?

Leonardo da Vinci is often credited with sketching an early ball-bearing mechanism.

In studies made around 1498, Leonardo explored how balls could reduce friction between moving surfaces. His drawings show balls held in a framework so they would not crowd together while rotating. This arrangement resembles the principle used by later rolling-element bearings.

The design was part of Leonardo’s broader investigations into friction, motion, and machines. He recognized that rolling contact could be more efficient than sliding contact, an idea important to gears, wheels, and rotating shafts.

Leonardo did not invent the complete modern ball bearing. Industrial bearings with standardized races, cages, and manufacturing methods developed centuries later. The historical claim is best stated carefully: his notebooks contain an early bearing concept, not a mass-produced modern component.