Two Thread Embroidery Attachment
This Page Compliments of Sharon Reese:
I don't know when Singer made the two-thread embroidery attachments, but I think that this one was made around the turn of the century judging by the style of the Singer lady's clothes.
According to Singer's "Machine Sewing" c. 1938, this attachment "is especially suited to the ornamentation of draperies, table scarfs and household furnishings in general. It is equally effective in outlining applique designs... The movement of the arms of the Embroiderer [the two curved arms] causes the two embroidery threads to cross each other in advance of each stitch so that they are fastened to the fabric by the needle and shuttle threads." The two straight arms in the picture on the bottom left are spool arms which hold the two spools of embroidery thread.