Jewel bearings are made from industrial grade synthetic diamonds such as rubies and sapphires. They are used to provide the bearing surface for fine quality mechanical watches and in small precision measuring instruments. There are number of jewel bearings in watches and the term 18 jewels means that there are 18 jewel bearings in the watch. Jewel bearings need to be manufactured and assembled by master craftsmen.

Components of watches such as balance wheels, pivots, and cap wheels are mounted in small bores that are lined with the jewels. Laser beams are used to drill and finish the holes. These holes are less than 1 millimeter in diameter. Jewel bearings have a very low coefficient of friction and this is important in deciding the accuracy of a watch. In addition, the bearings are extremely wear resistant, last for decades with no maintenance and are also non magnetic.

Use of jewel bearing is limited by their size and bearings greater than 10 millimeters are difficult to manufacture and are also expensive.