The jewels are synthetic sapphires or rubies, which have been drilled, chamfered and polished to serve as bearings for gears in watches, reducing friction of mechanical parts to a bare minimum. Generally speaking, on may say that a simple mechanical watch (hours, minutes and seconds hands) should include at least fifteen jewels located in the places most subject to wear due to friction. It should be fitted with a shock-absorbing system on the balance, a good quality balance-spring and an unbreakable spring.