For Singer models 66 class,99,185, 201, 240 and 250 series, 288, 327, 328, 329, 337, 338, 347, 348, 348,350 & 360 series, 401, 403, 404, 413, 416, 417, 418, 457, 466, 476, 477, 478, 500, 502, 503, 507,509, 513, 514, 518, 522, 527, 533, 534, 538, 560, school models 714, 717, 719, 724, 774, 776 with apollo type hook.  

It is recommended to use this type of metal bobbin if your bobbin case is also metal.  Use Class 66 Plastic bobbins if your bobbin case is plastic.

Outside diameter: 20.5mm - Height: 10.8mm - Axis diamter 6.2mm Alternative number 32522