2xAR and PAM 320/438 crystal sizes

[Unknownwatchmaker]

Does anyone know if the sapphire crystals found in the 320 and 438 are the same size? They appear to be the same size when measured with a metric tape measure, but this is a somewhat inaccurate method Long story short, I am considering getting an 2xAR crystal for the 320, but unsure if the available 2xAR 438/441 crystals in stock would also fit the 320.

I recently had a 2xAR crystal put in my 438, and it makes such a difference. The dial now looks black rather than grey from reflections. The only concern has been the durability of the AR coating. What are others' experience with the longevity of aftermarket 2xAR coatings?

Thanks!

 

[Unknownwatchmaker]

And sorry if this has been addressed elsewhere -- I attempted a search of the forums without luck. For the sake of contributing to the forums, here is another picture comparing the two that I just found in my camera roll: