Leonardo da Vinci is credited with sketching a ball bearing to reduce friction between moving parts.
Around 1498, Leonardo drew bearing systems containing balls that could roll between surfaces instead of allowing the surfaces to slide directly against one another. Rolling contact greatly reduces friction in many mechanical arrangements, making rotation easier and more efficient.
His design included a separator concept intended to keep the balls from touching and interfering with one another. That feature resembles an important principle used in modern bearings, although Leonardo’s sketch was not a complete industrial bearing in the modern sense.
Bearings had older precedents, and historians do not treat Leonardo as the inventor of every bearing principle. His importance lies in documenting a sophisticated Renaissance approach to rolling friction. Modern ball bearings use precisely manufactured balls, races, cages, and lubricants.