WatchOtaku : jewels


Jewels are little bits of colored corundum (the same stuff as sapphire; Al2O3) with a bit of dye. Originally real rubies and quite expensive, they are now a few cents each. Used as pivots and bearings, they are quite wear-resistant and with a bit of oil or grease will last for many years.

See the Orient post below for a decent explanation of the various types (cap, hole, pallet, and roller).

As a rule of thumb:

  • 17 jewels is the current minimum for an automatic movement, with 21 being more common.