Thanks all for your replies.? The embroidery attachment I am looking for is for the Singer 9w7 essentially a W&W D9.? It is illustrated, but very poorly, in the parts list I just put in the Files section of the board.? Part number 226301 and shown in Plate 11399.? The individual parts are also shown but it is a puzzle to reassemble them digitally.
Singer made a similar one for later models which are used with the ever popular Model 221 Featherweight.?
I have seen the two-thread model and it seems to have endured for many years including the change to a Singer side clamp type.?