Leonardo da Vinci sketched a ball bearing as a friction-reducing machine element.
His studies showed balls placed between surfaces so that motion would involve rolling rather than sliding. That principle reduces friction and helps moving parts turn more easily. The drawings are among the early documented examples of applying rolling elements to mechanical design.
Leonardo’s sketch should not be described as the complete modern ball-bearing industry. Practical bearings evolved through later experiments, manufacturing improvements, cages, lubrication, and standardized designs. The common historical claim is that Leonardo produced an early ball-bearing concept, not that he created every feature of the modern bearing used in machines today.