Schaublin 135 MT5 to B32 adapter ejection thread

Does anyone know what the actual size of the adapter thread is? It looks to be a bit under 52mm and 1.25mm pitch but I am having trouble matching it to make a new ejector ring. I don't have thread wires on hand and can only check the pitch with a thread gauge. Also the first few threads and maybe all of them are not full hight so it is hard to get the OD. Perhaps it is a full 52mm or something funny in inches?
Thanks
Luke

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