What type of mechanical bearing did Leonardo da Vinci sketch using balls?

Leonardo da Vinci sketched a ball bearing using balls to reduce friction between moving surfaces.

His design placed balls between rings or other supporting surfaces so that contact could occur through rolling rather than sliding. Rolling resistance is generally much lower than sliding friction, which makes the arrangement useful for rotating shafts and wheels. Leonardo’s notes show that he understood the practical problem of friction in machinery.

The sketch is often cited as an early ball-bearing concept, but it was not a complete modern bearing assembly. Without effective cages, seals, and precise manufacturing, balls can bunch together or fall out. Modern bearings depend on those additional parts as well as carefully finished materials.

Leonardo did not invent the only form of bearing. Plain bearings and other rolling designs existed in various historical settings, and later engineers developed ball bearings for industrial machines. His contribution is best understood as an early, clearly recorded mechanical solution to reducing friction.