o ring seal

[oilyfinger]

I bought  0.5mm O ring for my watch but the back screws down farther than it used to, what is the normal thickness of o ring on a Seiko?

[Waggy]

O-rings are a bit tricky, if you are replacing with a generic brand then it may be necessary to use a different thickness than the original. O-rings are manufactured with different hardness (durometer) depending on their material and how they are made, therefore, a 0.5mm o-ring from seiko may compress more or less than a 0.5mm o-ring from Omega depending on who made the o-ring for them. In addition to this, measuring the original may not always be the best idea as they tend to dry out and flatten over time and become brittle essentially changing size.

I have a range of thicknesses and sizes, you can buy them relatively cheaply from ebay/amazon.ali etc (see attached example from Amazon).

I think 0.5mm is a little on the small side, I usually start with a 0.7mm and then take it from there, also remember to use a small amount of silicone, this keeps the o-ring flexible and also helps keep it in place when closing up the watch. Another trick is to first drop the o-ring in a cup of hot water, this will make it more flexible and less likely to snap when you are stretching it into position.

Hope this helps!

[oilyfinger]

Yes a very understandable and helpful reply. My problem arose because the watch is an old one of mine, that I've changed the battery several times, the last time the o ring was so distorted i discarded it, when i came to change the battery again I had no idea what the thickness should be i'll try 0.7mm.