A mechanical movement contains watchmaker’s stones that reduce friction, and hence wear, to a minimum. The rubies that were originally used have long since been replaced by synthetic sapphires. These jewels, as they are still called, are turned, polished and drilled to serve as bearings for the different gears of a watch.
In general, a standard mechanical watch displaying hours, minutes and seconds should in principle contain at least fifteen jewels located in the places most subject to wear caused by friction. It must be fitted with a shock-absorbing system on the balance, containing a jewel.