Sizing a caseback O-Ring replacement

[linux]

I not yet had to replace a caseback O-Ring gasket until yesterday when I cracked open an old quartz watch to swap out the battery.  When I went to button it up I noticed that the O-Ring was protruding from the case, obviously stretched.  The watch is about 10 years old and I guess they just lose their elasticity.

So I quickly realized I couldn't order the OEM part and that even if I did it'd cost more than getting a bag of 100 sorted gaskets.  I measured the diameter of the caseback with my micrometer and it measured 38.85mm (large watch) which would be the inner diameter of the gasket.  The thickness was a bit vague.  Esslinger had a video which says to measure the height of the outer slot where the gasket will fit in and that came to 1.4mm but when I measured the actual gasket it was more like 1mm.

I'm probably over-thinking this but wanted to see how people approach this.  I'll likely just order a pack of 150 1mm thick O-Ring gaskets from Esslinger.

Edited September 12, 2024 by linux

[mikepilk]

I'm not sure gaskets are supposed to be a tight fit or not. I'd buy 38.5 and 39mm (if available) and try both. 

I bought a pack of 100 gaskets (Indian) from Cousins. I don't think I've ever used one as the quality is poor. Unless you know they are good quality (Swiss) I would advice  against, and just buy the sizes you need.  ISO Swiss ones  are only about £2 per pack of 2 from Cousins. I usually buy a couple near the size I want, and you soon build up a useful stock. 

[rehajm]

11 minutes ago, mikepilk said:

I'm not sure gaskets are supposed to be a tight fit or not. I'd buy 38.5 and 39mm (if available) and try both. 

I bought a pack of 100 gaskets (Indian) from Cousins. I don't think I've ever used one as the quality is poor. Unless you know they are good quality (Swiss) I would advice  against, and just buy the sizes you need.  ISO Swiss ones  are only about £2 per pack of 2 from Cousins. I usually buy a couple near the size I want, and you soon build up a useful stock. 

As I just spent a few hours looking through case screws I’d say this is good advice for screws, gaskets, jewels… Just measure as best you can and go with high quality graded, buy a size larger &/or smaller which will build a collection of more appropriately sized spares. 

Edited September 13, 2024 by rehajm

[AndyGSi]

What's the watch and is it an O-Ring or a Flat Rubber?