This is an original Singer low shank adjustable zipper foot, part # 161127. It fits Singer models 15, 27, 28, 66, 99, 101, 185, 192, 201, 206, 221, 222, 237, 239, 242, 247, 248, 252, 257, 285, 306, 319, 327, 328, 329, 337, 338, 347, 348, 353, 360, 413, 418, 457, 476, 477, 478, 513, 533, 534, 543 and many more low shank machines.
This foot makes it easy to place stitching close to a raised edge, making it useful for cored seams. It can be adjusted to either the right or the left side of the needle, and the hinge allows it to ride over pins, heavy layers of fabric or cross seams.