Does the watch you're repairing have a gasket? When you open the case-back, the gasket needs to be replaced if it's worn out. Before ordering a new one, you need to know its size. This guide shows you how to measure a watch gasket so you can replace it safely.
Before measuring the gasket, you'll need to open the watch. Our online shop carries a range of watchmaker tools to open the case (snap-back, screw-back, screwed, etc.).
Verre-de-Montre accepts no liability for any damage resulting from a gasket change.
What is a watch gasket?
A watch gasket is the seal that makes a watch water-resistant. Located on the case-back, the crown, or around the crystal, the watch gasket comes in different shapes, materials and sizes to fit each watch.
The different types of watch gasket
Before ordering a gasket, work out which type you need. If your watch came with an O-ring (torus) gasket originally, you must replace it with the same kind.
O-ring (torus) gasket
An O-ring is the most common watch gasket - circular (although other shapes exist) and made of rubber. It seals the case-back against the case, keeping water and dust out of the movement.
Flat gasket
The flat gasket, as the name says, has a flat profile rather than a round one. Like the O-ring, it sits between the case-back and the case to seal the watch. Usually circular, sometimes shaped, made of rubber. If your watch originally had a flat gasket, replace it with the same kind.
Red gasket (Sanfil)
The red gasket, also known as "Sanfil", is rigid. Famous for its strength, it offers solid protection against water and dust. The colour makes it easy to identify when replacing it. Unlike rubber gaskets, it doesn't need lubrication.
Silicone gasket
Silicone gaskets are found on modern, high-end watches. This style is designed to handle pressure and moisture, and sits on the case-back.
Crystal gasket
Designed specifically for the crystal, the crystal gasket is rigid and seals the front of the case. It's used with mineral or sapphire crystals. Like the Sanfil, it doesn't need lubrication.
Crown gasket
The crown gasket is critical for water resistance. Water can also get in through the crown and stem, damaging the movement. The crown gasket adds another layer of protection. Made of rubber, it sits inside the crown.
Measuring a watch gasket
You'll need a pair of calipers from our online shop.
Once the watch is open and the gasket is visible, place the calipers across the groove in the case-back. The reading is the gasket's inner diameter. If the case-back has no groove, measure the outside of the case-back edge that seats into the case.
To measure the gasket thickness, gently close the calipers on the gasket without squeezing it.
Tip: depending on the watch, an error of around 0.10 mm in thickness and 0.50 mm in diameter is acceptable.
Gasket diameter
Reading: 35.80 mm
Gasket thickness
Reading: 0.60 mm
Buy a watch gasket
Now that you know how to measure a watch gasket, browse our online shop categories to pick the right part. The main size listed on each product page is the inner diameter.
Gasket guides
Our guides help you with everything around watch gaskets.
- Change a watch gasket - illustrated guide
- Open a snap-back watch - illustrated guide
- Open a screw-back watch - illustrated guide
Tools for watch gaskets
Browse our affordable watchmaker tools and accessories to change a gasket with confidence.