A gasket is a sealing element placed between two components to ensure their watertightness (e.g., the caseback gasket ensures the watertightness between the caseback and the case). Their shape, cross-section, and material can vary depending on the watch’s design or component and the gasket’s function.

The range of plastics used for gasket manufacturing is quite extensive today. The material can be elastic (e.g., vulcanized rubber) for caseback or bezel gaskets, such as O-rings (round section). They can be rigid with an “I” section for sealing a crystal to its caseback or bezel. In such cases, compressing the gasket during the crystal installation provides the required watertightness and secures the crystal to the bezel.

By definition, the gasket is the last line of defence against external elements. Therefore, it must be resistant not only to dust and moisture but also to UV rays or common chemicals. Nevertheless, the lifespan of gaskets is limited, and their condition needs to be periodically checked during maintenance. When space for a gasket is too limited, or when the shape of the contacting components is complex, specific adhesives may be used. They will ensure the bonding of the connected components and their perfect watertightness.

The materials used for gasket production in the beginning were cork, leather, and lead. These materials persisted until the middle of the 20th century before being replaced by elastomers and plastics. Their properties, resistance, and longevity have continued to evolve alongside the discovery and development of new materials.

The first patents dealing with the water resistance of watches emerged at the end of the 19th century. The initial waterproof watch, a Depollier, became the subject of military research in the context of the First World War starting in 1915. It underwent testing in 1918 and was subsequently ordered by the United States War Department in 10,000 units through purchase order #160615. That was realised thanks to the patent dated May 15, 1917. This patent was approved by the United States Patent Office four months later, on September 11, 1917, under the number 1,239,467.

Gaskets are mainly produced by specialized subcontractors. Depending on their shape and purpose, various materials can be used. Injection is used to produce elastic O-ring gaskets. When the material is sufficiently hard and their cross-section is complex, gaskets will be machined from bars or discs of raw material. Finally, stamping or laser cutting are preferred methods for the production of flat gaskets.