Component record · Case
Gasket (Case Seal)
VerifiedA ring or washer, generally of synthetic rubber or a similar elastomer (historically sometimes cork, felt or shellac-impregnated fibre in early attempts at sealing), compressed between case components to exclude moisture and dust.
What it does
Seals the joints of a case — between case back and case band, around the crown and crystal, and sometimes around pushers — so that water resistance ratings claimed for the watch are actually achieved.
How it works
A gasket sits in a groove or against a shoulder machined into the case, and is compressed when the mating part (case back, crown, or crystal) is fitted, forming a barrier that resists the ingress of water and dust under the pressures the watch is rated to withstand.
Because rubber and similar elastomers harden, shrink and lose elasticity with age and exposure to solvents, heat and skin oils, gaskets are considered consumable service items that should be inspected, lubricated with an appropriate silicone grease, and replaced at routine servicing rather than assumed to remain effective indefinitely.
Water resistance ratings apply only to a watch in its as-tested, as-sealed condition; a watch with a perished, missing or incorrectly sized gasket will not achieve its rated resistance regardless of the case's original design.
Evolution
Sealing materials and case engineering steadily improved through the twentieth century, moving from simple friction-fit soft materials to precision-moulded synthetic rubber gaskets and, in high water-resistance designs, multiple redundant seals at each joint.
Known variations
- Case-back gasket (flat ring or O-ring type)
- Crown gasket(s), sometimes multiple in high-water-resistance screw-down crowns
- Crystal gasket, seating the crystal against the case or bezel
- Pusher gaskets on chronograph and similar multi-pusher cases
Identification for collectors
- A visible rubber ring at the case-back joint or around the crown and pushers on disassembly
- A hardened, cracked, flattened or missing gasket is a routine servicing finding and a common cause of moisture ingress and dial/movement corrosion
Common failure modes
- Age-hardening and loss of elasticity, compromising the seal even without visible damage
- Compression set (permanent flattening) after long periods under load
- Damage from solvents or improper lubricants used during a careless service
Related photographs
No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- de Carle, D., Practical Watch Repairing
Where sources disagree, the disagreement is stated rather than resolved silently.