Vintage Singer sewing machine low shank bias binder / binding foot. This attachment came with a 1940's or 50's 221, but will fit many other low shank machines as well.  With the Binder Foot, you can apply bias binding to an unfinished edge in a single operation.  Such binding can be a color trim for children's clothes, aprons, or household textiles. Or it can be a practical finish for seam edges that might ravel.  If you buy ready-made bias binding, use No.5, which will be 15/16 of an inch wide and will come already folded.  If you can made the binding yourself, be sure to cut it 15/16 of an inch wide on the true bias.