Which Leonardo da Vinci design is an early example of a ball bearing?

Leonardo da Vinci's rotating-ball mechanism is recognized as an early ball-bearing design.

Leonardo studied friction and machine motion in notebooks from the late fifteenth and early sixteenth centuries. One drawing shows balls arranged so that surfaces can move against one another with less sliding friction. The basic principle is the same as a ball bearing: rolling elements separate moving surfaces and make rotation easier.

The design is often described as an invention of Leonardo, but ball bearings were not manufactured in the modern standardized form during his lifetime. His sketch demonstrates the principle rather than a complete industrial product. Practical bearings required later advances in materials, precision machining, lubrication, and manufacturing.

A ball bearing differs from a roller bearing because it uses spherical balls rather than cylindrical rollers. Both reduce friction, but their load capacities and motion characteristics differ. Leonardo's study belongs to his broader investigations of gears, shafts, pulleys, and mechanical resistance.