Leonardo da Vinci sketched a ball bearing with balls between moving surfaces.
His studies of friction include a design in which loose balls separate two rings or surfaces. The arrangement allows the parts to move with rolling contact instead of rubbing directly against each other, reducing friction. The drawing is usually associated with Leonardo’s work on mechanical principles around the late fifteenth century.
Leonardo did not invent every later form of bearing, and his sketch was not a mass-produced modern bearing. It is better understood as an early documented proposal for using rolling elements to reduce friction. Practical bearings evolved gradually, with later designers improving materials, cages, lubrication, tolerances, and manufacturing methods.
A ball bearing is different from a plain bearing, where surfaces slide against one another, and from a roller bearing, which uses cylindrical or tapered rollers. Leonardo’s design matters because it clearly applies the basic principle behind modern ball bearings: rolling elements carry the load while limiting sliding friction.