This is a slide bobbin cover plate for a Singer Sewing Machine models 401 (401A), 403 (403A), 404 (404A), 500 (500A), 503 (503A), 600, 603, 604, 620, 620E31, 625, 626, 628, 629, 630E, 635, 636, 638, 639, 640E, 645, 646, 648, 649.
This will NOT fit a Singer Featherweight.