Singer Simanco (#121547) Great Britain Under Braider. It will fit on almost all vintage black SINGERs like:

15k 28k 128k 66k 99k 201k 201-2 Featherweight 222 221

A very clever and useful attachment for decorative embroidery.  This attachment is specifically designed to help with under braiding, providing smooth and precise results. Ideal for crafters and seamstresses, this Singer accessory is a reliable and high-quality addition to any sewing machine. This item is in overall good vintage condition. Please see all pictures for condition details and dimensions.

Shelf A Organizer 1