Can anyone help ID this. Never saw one like this!
The early (1912-1913) Diamond Disc product line had a number of machies with oxydised copper brightwork, of the sort that Edison had previously used on his Idelia, Opera, and Amberola cylinder phonographs. You have an early "Balance" lateral (std. 78) adaptor for one of these rather scarce A series phonographs. Note the unusual embossed aluminum diaphragm known as a Mobley diaphragm form the man who develped it for use in cylinder reproducers.
I suspect that you wuld find this to be a fairly valuable item.