Girard Perregaux gyromatic caseback

[noirrac1j]

Hello my fellow watch goons,

I need help with a caseback for a Girard Perregaux gyromatic 47 AE (same at ETA 1256)

The problem is I don't know that name of suchg a caseback item. It is a notched metal ring that has threads. I found a Bulova ring to show as an example:

 

and this would go into the case (conventional inner threads) and holds down a traditional caseback--but that  has no threading.

 

The size of the case is 30.25" at the inner diameter, so I am guessing that is the size ring I need. As I said, the ring I have shown is from a smaller Bulova watch. Any info on how to get aftermarket or equivalent would be appreciated. I know you guys like pictures, so here is the front of the watch.

 

 

Regards,

J

 

 

 

Edited March 28, 2017 by noirrac1j