Why accurate gasket measurement matters
On watches with a round bezel, the crystal gasket holds the crystal in place and contributes to water resistance. Accurate measurement is essential so you order the right reference and avoid having to replace the crystal as well.
Browse our catalogue of watch crystal gaskets once you have your measurements.
Required tools
- Digital caliper with internal measurement jaws
- Watchmaker tweezers
- Watchmaker loupe (x5 or x10)
These items are available in the watchmaking tools category.
Measurement steps
- Remove the crystal and the old gasket so the bezel groove is fully accessible.
- Locate the ledge at the bottom of the bezel: this is where the gasket and crystal will rest.
- Insert the inside jaws of the caliper against the wall just above this ledge.
- Take the measurement at two or three different positions to confirm the result.
- Round to the nearest tenth of a millimetre.
Choosing the right reference
On joint-de-montre.com, every crystal gasket lists two measurements:
- Outside diameter: matches the inside diameter of the bezel measured above.
- Inside diameter: matches the diameter of the crystal that will sit inside the gasket.
If your existing crystal does not match the inside diameter of the gasket, you will need to order a suitable crystal. Gasket thicknesses vary by reference.
Measure twice, order once: the golden rule of the amateur watchmaker.
Common mistakes to avoid
- Measuring the crystal diameter instead of the bezel groove
- Forgetting to take the measurement at several positions
- Confusing the inside and outside diameters of the gasket
FAQ
How precise should the measurement be?
A tenth of a millimetre is enough. Use a digital caliper to avoid reading errors.
Do I always need to replace the crystal too?
Not necessarily. If the new gasket thickness differs from the old one, a suitable new crystal will be required.
What if the bezel is oval or tonneau-shaped?
The caliper method still works, but you have to measure both the long and short axes. A custom order is preferable.
How do I fit the gasket once I receive it?
Follow our guide fitting a new watch crystal gasket.