A gasket, or seal, is a part placed between two components of a watch to keep the joint water-resistant. It is usually a rubber or synthetic O-ring. It matters because it keeps water and dust out of the case. A worn gasket stops doing that job.
Where are the gaskets in a watch?
Gaskets sit wherever two parts of the watch meet and the joint must stay water-resistant. The crystal is one such joint. Many watches seal the crystal into the bezel with a thin gasket or a cement ring. The crown tube is another. This is where the winding stem leaves the case. Dive watches and other high-performance watches often use several gaskets together, so that more than one seal guards the case.
What are watch gaskets made of?
Modern gaskets are usually nitrile rubber, silicone or another synthetic compound. Some are made of Teflon instead. Elastic O-ring gaskets are made by injection moulding, in which the material is forced into a mould and sets in shape. Crystal gaskets are a different type. They can be stiff. Cut through, they show an upright with a flat bar across the top and the bottom, like a girder. The elastic O-rings used elsewhere in the watch are round in section.
Why do gaskets need replacing?
Gaskets wear out over time. For this reason, watchmakers routinely fit new ones at every service, even when the watch has never been in water. A watch kept dry still needs fresh seals. The gasket at the crown tube needs particular attention. It is often the weakest point of the seal and a common place for moisture to get in.
Where it comes from
The first patents for water-resistant watches appeared in the late 1800s. The earliest watch gaskets were mostly made of cork, leather and lead. These did the same basic job as a modern O-ring: closing the gap between two parts of the case. By one account, a Depollier was the first waterproof watch, and the military began studying it in 1915.
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