What part number has my SEIKO crystal?

[VWatchie]

Hmm... would it be any idea to try with either or both of a) and b)?

a) 2.5 mm thick (0.08 too thin) 31.0 mm diameter" (0.02 mm too wide)
b) 2.5 mm thick (0.08 too thin) 30.9 mm diameter" (0.08 mm too narrow)

CousinsUK.com have them and as far as I can see there's a chamfer of equal type on both sides? MSH Sternkreuz is £2 each and Cousins is 0.95 each. I'll be using the original gasket. I suppose there's a risk I would mangle the gasket with the crystal being slightly too wide. Or, since the gasket is already somewhat depressed it will slide right in? Any disadvantage compared to the other of your options if I can get it to fit? What's the difference between Cousins own crystals and the MSH Sternkreuz?

[JohnD]

27 minutes ago, VWatchie said:

Hmm... would it be any idea to try with either or both of a) and b)?

a) 2.5 mm thick (0.08 too thin) 31.0 mm diameter" (0.02 mm too wide)
b) 2.5 mm thick (0.08 too thin) 30.9 mm diameter" (0.08 mm too narrow)

CousinsUK.com have them and as far as I can see there's a chamfer of equal type on both sides? MSH Sternkreuz is £2 each and Cousins is 0.95 each. I'll be using the original gasket. I suppose there's a risk I would mangle the gasket with the crystal being slightly too wide. Or, since the gasket is already somewhat depressed it will slide right in? Any disadvantage compared to the other of your options if I can get it to fit? What's the difference between Cousins own crystals and the MSH Sternkreuz?

Don't think either of those is suitable, if there is an equal chamfer both sides. The gasket side needs to be a very slight chamfer, just to aid entry and the bezel side needs to be a large chamfer to stop interference with the bezel. Also a 30.9mm one it will fall into the gasket, 0.1mm is a VERY big difference . If a 31.0mm crystal is dead size then it will still be only 0.020 of a millimetre larger than the one that you have removed and the gasket will allow for that small difference.

The SternKreuz crystal has the tiny chamfer on one side and the large chamfer on the other, the same as the generic 3mm one I linked to before...

Edited June 5, 2020 by JohnD

[jdm]

56 minutes ago, VWatchie said:

CousinsUK.com have them and as far as I can see there's a chamfer of equal type on both sides? 

As mentioned above, I don't think that regular flat have enough chamfer to clear the bezel. Just look at your picture to see how it reflects the chapter ring. It is very similar to the SKX diver's crystal 315P15HN02. If you want to try anyway the size to order is definitely 31mm.

Edited June 5, 2020 by jdm

[VWatchie]

On 6/5/2020 at 9:11 PM, JohnD said:

The SternKreuz crystal has the tiny chamfer on one side and the large chamfer on the other, the same as the generic 3mm one I linked to before...

I had a good look in the Sternkreuz catalog and found the above crystal which seems near my original crystal (Ø30.98 mm 2.58 mm). Looking at the picture it looks like it has both the heavy chamfer and the thin chamfer, right? Now, you have already established that the 31 mm in diameter ought to fit well in the original gasket, but what about the missing 0.18 mm in thickness?

Searching for "XMF 310.853" using Cousins' "Glasses by Sternkreuz Reference" I found this:

Now, £18 (including tax and shipping) is quite a bit of money, but if it works I feel it would be worth it.

So finally, and I promise not to nag you anymore , do you think the above crystal will be a good replacement?

Edited June 6, 2020 by VWatchie

[JohnD]

3 minutes ago, VWatchie said:

I had a good look in the Sternkreuz catalog and found the above crystal which seems near my original crystal (Ø30.98 mm 2.58 mm). Looking at the picture it looks like it has both the heavy chamfer and the thin chamfer, right? Now, you have already established that the 31 mm in diameter ought to fit well in the original gasket, but what about the missing 0.18 mm in thickness?

Searching for "XMF 310.853" using Cousins' "Glasses by Sternkreuz Reference" I found this:

Now, £18 (including tax and shipping) is quite a bit of money, but if it works I feel it would be worth it.

So finally, and I promise not to nag you anymore , do you think the above crystal will be a good replacement?

Well, 0.18mm is  7 thousandths of an inch  so about two thicknesses of a human hair... not going to make a great difference is it?

[VWatchie]

2 hours ago, JohnD said:

Well, 0.18mm is  7 thousandths of an inch  so about two thicknesses of a human hair... not going to make a great difference is it?

No I didn't think so, but I've learnt to never take anything for granted,  and I will assume you would have told me if you saw any other problem with this crystal.

Well, thank you and @jdmfor all support and information. Immensely appreciated!