How do I select the correct replacement glass

[NigelB]

I have narrowed down the glass for my Roamer Vanguard to the 311802 on roamers chart shown below as X7311 but am having trouble selecting the correct replacement from the many different ones on the cousins site, can any one point me in the right direction please as there isnt a cross reference for this number I can find.

The current glass has a silver coloured metal ring fitted inside and has the following dimensions

OD = 30.60 mm

ID = 27.95

Height 4.34 mm

Thickness = 1.22 - 1.26 mm varies over the surface of the glass, the middle being the thinnest

 

[WatchMaker]

With a ring inside the crystal this is an armed tension type. The Sternnkreuz 'G22' catalogue covers these which you can download at http://www.sternkreuz.de/accordion/assets/Sternkreuz_Gesamtkatalog G22.pdf

Whilst for the Sternkreuz 'ST'' range Roamer does have some specific citations (p25), for the 'ATC' range you need none are mentioned. Almost certainly therefore you'll be fine with a standard ATC crystal that meets your measurements.

The usual advice is to go 0.1 larger than the outside diameter measurement you've taken. This means when you release the crystal, after it has been gently 'squeezed' in the claw removal/fitting tool, it makes a nice tight fit.

Since you're using Cousins your best bet is going to therefore be https://www.cousinsuk.com/product/standard-chrome-ringed-glass-atc# and the 30.7mm size.  

 

[NigelB]

Thanks @WatchMaker that makes perfect sense, as someone new to this it is just so confusing with the range of different crystals available. 

I have ordered the Crystal ( 30.7mm ) you suggested along with a few other bits I need.

[WatchMaker]

No problem ... and I agree this isn't always the easiest subject - especially where dimensions like dome heights aren't often mentioned!

I hope the 30.7 works out. I should have qualified my original reply with a dependency on how tight your existing 30.6 is for that 0.1 increase suggestion. If it's already a very tight fit then the 30.6 might have been okay but usually the 0.1 increase over a measured outside diameter is a useful guideline. If you've already ordered then you can always take some fine abrasive paper and gently take away any fraction off the 30.7 should this be necessary!

[NigelB]

After the original removal with the claw tool, the crystal I removed was a tight press fit by hand and popped out again with gentle pressure from inside, so I think your idea of the extra 0.1 mm oversize should make it a good fit once in place.

I'll post back again once I have the crystal in hand and fitted into the case.