I have a Seiko V158-0AD0 which works very well, and I recently noticed the crystal was scratched more than the case… so a strong hint that it is an ordinary mineral glass crystal.
Searching the net, I could find that the Seiko part number for the original crystal is 310P03HN0 which indicates a diameter of 31.0mm but it does not have the thickness encoded simply. I could not find any articles giving the thickness of the part… so measurement was needed.
Above, the original crystal measures 1.6mm. A ‘standard’ 1.5mm sapphire crystal should be just fine.
As this is a pretty new watch, and I have a 31.0×1.5mm sapphire crystal in stock, I replaced it on the spot, cleaned up with a bit of Rodico, some grease on the seal and reassembled the watch. I did not bother pressure testing it, it doesn’t go swimming these days.
The 1.5mm crystal is thick enough to be just proud of the bezel.
- To release the stem look for the dimpled lever below the back plate with the stem fully inserted, depress it well and the stem comes out easily.
- Once the stem is out, place a case cushion over the movement, invert it and lift the case clear of the movement.
- The crystal presses out with the bezel in place.
I ordered a couple more sapphire crystals for stock, A$18 for two with shipping from Aliexpress.