I've come across a few of these types of crystals and have no idea what they're called

[Max50916]

What type of crystal is this? The case pushes through the back and the crystal essentially hugs the outside of a lip at the top of the caseback. I've come across there before but have always been lucky enough to just polish the existing one and have never replaced one. The one on this watch has some bizarre crazing going on and it definitely needs to be replaced, but I'm not sure how to find one. This particular crystal measures 29.4mm in diameter. I tried taking the ring out of a tension ring crystal as a kind of work around but the smooth space where the ring was isn't deep enough to hug the whole lip. Thanks for whatever advice you can give!

[Kalanag]

I think it’s a „Sternkreuz XS Stülpglas“.

This may help:

 

Edited May 6, 2022 by Kalanag

[Kalanag]

I forgot to mention: Medana = Roamer = MST = Meyer & Stüdeli

Edited May 7, 2022 by Kalanag

[spectre6000]

I had one of those on a 40s Certina a while back. Major PITA to find a replacement... I took very careful measurements of all the critical dimensions, then looked through the crystal manufacturers' catalogs. All of the required measurements aren't always published, and I ended up calling the company that had the closest match across a small number of the specs that were published, and told them the third critical dimension. She did some digging, and came back with a couple that were close on either side. I got both, and ended up needing to carefully reduce the outer dimension until it fit snug, but not so snug I couldn't get the case open/closed again. Not my favorite means crystal replacement, but doable.

[Max50916]

On 5/6/2022 at 3:59 PM, Kalanag said:

I think it’s a „Sternkreuz XS Stülpglas“.

This may help:

 

Thank you so much! Very helpful!

On 5/7/2022 at 12:12 PM, spectre6000 said:

I had one of those on a 40s Certina a while back. Major PITA to find a replacement... I took very careful measurements of all the critical dimensions, then looked through the crystal manufacturers' catalogs. All of the required measurements aren't always published, and I ended up calling the company that had the closest match across a small number of the specs that were published, and told them the third critical dimension. She did some digging, and came back with a couple that were close on either side. I got both, and ended up needing to carefully reduce the outer dimension until it fit snug, but not so snug I couldn't get the case open/closed again. Not my favorite means crystal replacement, but doable.

That's a good idea, thank you so much! 

[watchfellow]

On 5/7/2022 at 9:12 AM, spectre6000 said:

I had one of those on a 40s Certina a while back. Major PITA to find a replacement... I took very careful measurements of all the critical dimensions, then looked through the crystal manufacturers' catalogs. All of the required measurements aren't always published, and I ended up calling the company that had the closest match across a small number of the specs that were published, and told them the third critical dimension. She did some digging, and came back with a couple that were close on either side. I got both, and ended up needing to carefully reduce the outer dimension until it fit snug, but not so snug I couldn't get the case open/closed again. Not my favorite means crystal replacement, but doable.

May I ask what was the method you used to reduce the outer dimension of the crystal? I am in a similar boat, but am not sure of the best way to go about it.

[spectre6000]

Either scraped with a razor blade (hold it at a 90° angle to the surface and it'll pull off fine shavings) or fine grit sandpaper. Don't recall what I ultimately went with... followed by crystal polish. Didn't need much.