The watchmaking O-ring gasket in NBR nitrile rubber by the Swiss brand ISOSWISS, with a thickness of 1.20 mm (reference jointTOni-1-20), is an essential horological spare part for restoring the water resistance of a watch case. This round-section O-ring sits in the groove of the case-back - referred to as the case-back gasket - or under the bezel for press-fit crystal designs. It protects the movement from water, dust, humidity and perspiration.
Technical specifications
- Section thickness: 1.20 mm
- Catalogue reference: jointTOni-1-20
- Family: O-ring gasket - round profile
- Material: NBR nitrile rubber (Buna-N), FKM / Viton version available on request for high-temperature applications
- Brand: ISOSWISS (Swiss-made)
- Colour: black
- Inner diameter: very wide range in the drop-down list (from 13 mm to over 50 mm)
- Packaging: sold individually or in lots
- Compatibility: standard watch cases, screw-down and snap-on backs, water-resistant watches from 3 ATM to 20 ATM
- Service range: -20°C to +100°C in NBR (up to +200°C in FKM)
What is this watch gasket used for?
The 1.20 mm O-ring is the number-one sealing component of a wristwatch. Compressed between the case-back and the middle case (case-back gasket) or between the crown and the tube (crown gasket), it ensures that the watch preserves its original water resistance - typically 3 ATM (splash-proof), 5 ATM (showering), 10 ATM (swimming) or 20 ATM (recreational diving). After every opening of the case - battery change, movement service, polishing - the gasket must be replaced as a matter of principle, because the rubber has been compressed and has lost part of its elasticity.
When should you replace your O-ring?
Several signs indicate that a new gasket is needed: condensation under the crystal, traces of moisture inside the case, loss of pressure on the water-resistance tester, or simply because the watchmaker recommends a systematic change every two to four years, or after every battery change. A hardened, cracked, oval or sticky gasket must be replaced before the watch is returned to service. A full overhaul also covers replacement of the crown gasket and, where fitted, the crystal gasket.
How to fit a 1.20 mm O-ring gasket
The procedure is straightforward: 1) open the case with a three-prong tool for screw-down backs, or with a case knife for snap-on backs; 2) lift the old gasket out with anti-static tweezers; 3) degrease and clean the groove with benzine or isopropyl alcohol; 4) measure the inner diameter of the used gasket with a digital caliper to confirm the size to order; 5) lightly lubricate the new O-ring with horological silicone grease (Moebius 8217 type) to preserve its elasticity and to ease compression; 6) drop the gasket into the groove without twisting it; 7) close the case-back and test water resistance. See our illustrated guides: Replacing a watch case-back gasket and Lubricating a watch gasket the easy way.
Quality and material
NBR nitrile rubber (acrylonitrile-butadiene) is the traditional choice for watch gaskets: excellent water and mineral-oil resistance, good pressure rating, broad temperature range, affordable price. For more demanding applications (heat, ozone, solvents) we also offer gaskets in FKM (Viton) and EPDM. Every gasket is supplied in a labelled individual sachet and is stored away from light and ozone to preserve flexibility until use.
Frequently asked questions
How do I know the size to order? Measure the old gasket with a caliper: the figure to record is the inner diameter. The section thickness (1.20 mm) is set by your product choice in the drop-down. See also Measuring a watch gasket before buying.
Is it really necessary to lubricate the new gasket? Yes. A dry-fitted O-ring cracks quickly and loses its seal. Use horological-grade silicone grease (Moebius 8217) in a very thin film.
NBR or silicone - which to choose? For most watches exposed to sea water, showering or swimming, NBR is the standard; silicone is reserved for watches subjected to heat (sauna). For extreme temperatures or solvents, choose FKM (Viton).
