This is a genuine vintage Singer Attachment - the Cloth Guide or sometimes referred to as either the Seam or Hem Guide.
The cloth guide attachment is a help in straight stitching. The guide is fastened to the machine by means of the thumb screw (included) into the bed of the machine as shown in the photograph. Attachment can be adjusted to various distances from the needle as desired - perfect for clearly establishing the 1/4" seam allowance for quilt piecing!
Are you adhering masking or scotch tape to your machine to use as a hem guide? Begin using this much more reliable Singer tool. After all, that's what it was designed for! The cloth guide screws down very tight and secure.
This attachment fits the Singer Featherweight 221, 222K and all other vintage Singer Sewing Machines (i.e. 15, 27, 28, 66, 99, 185, 127, 128, 192 Spartan, 201, 206, 221, 222, 237, 306, 319, 320, 328, 401, 403, 404, 500, 503, as well as many other brands besides Singer).