Sizing tonneau crystal over or under? (Bulova)

[mbwatch]

Forgive the novice question. I have a 1940s Bulova which is either an "Aviator" or possibly an "Alderman" model. I have found some old GS crystal lists that identify these models as MT293 for the Aviator and MT298 for the Alderman. The measurements of each are given.

Measuring my case, it falls right between them. I measure at the widest part of the curves 22.5x20.4mm. The two crystal options are each 0.2-0.3mm larger and smaller in the two dimensions than my measurements.

Should I be buying acrylic at 22.3x20.1 and gluing it in or buy larger at I think 22.8x20.8 and squeezing it in? I believe I have seen examples where a crystal lift could compress noncirclular acrylic.

Edited March 8 by mbwatch
Sp

[AndyGSi]

What's the case reference.

Edit

I presume you've not got the old one but do you know if it curves in both directions?

Also looking at the shape of the bezel I'd say it was an Aviator due to the step which isn't on the Alderman.

Edited March 8 by AndyGSi

[mbwatch]

1 hour ago, AndyGSi said:

What's the case reference.

Edit

I presume you've not got the old one but do you know if it curves in both directions?

Also looking at the shape of the bezel I'd say it was an Aviator due to the step which isn't on the Alderman.

This is my first time with a vintage Bulova and I missed a detail. There's a "48" printed on the movement which is a cal 10BC. And the only number on the case is a serial 9082810. The inside of the case just reads "BULOVA 14k rolled gold plate bezel stainless back New York." So pretty clearly a 1948 movement. Any chance the 9 starting the serial is 1949?

It came in a job lot box without a crystal, but the edges of the bezel do curve in both directions. The short side is very slightly curved.

Clicking through the Aviator and Alderman models, I don't see any Aldermans with a 10BC but the Aviators mostly appear to use that movement. https://mybulova.com/watches/1949-aviator-4800

[AndyGSi]

So yes it's a 1948 movement in a 1949 case.

I asked about the curve as there's this that matches your sizes better but is only curved the length.

Edit

Just found this so maybe your measurements are slightly out.

 

Edited March 8 by AndyGSi

[mbwatch]

34 minutes ago, AndyGSi said:

Just found this so maybe your measurements are slightly out.

 

That is likely, because my calipers are terrible. I will order the GS CMT293, and if it doesn't quite work I can move up to the 298. Back to my original confusion - should I expect this crystal to snap in place or will I be gluing it? Thanks for your help.