Leonardo da Vinci is often credited with sketching an early ball-bearing design for reducing friction between moving parts.
Around 1498, Leonardo made drawings showing balls placed between rings so that the balls could roll while keeping the rings from rubbing directly against each other. This principle is the basis of a ball bearing: rolling contact replaces much of the sliding friction found in a plain bearing.
The drawing appeared in Leonardo’s studies of mechanics and was not necessarily a finished industrial device. Bearings and related friction-reducing mechanisms had earlier precedents, so Leonardo should not automatically be described as the sole inventor of every bearing technology.
His importance lies in clearly illustrating a practical arrangement that resembles modern ball bearings. Industrial production of standardized bearings came much later, after advances in precision manufacturing.