Singer 404 Slant shank bobbin cover slide plate #179015.  Used working repair/ replacement part.  Should work on many Singer models including:
401, 403, 403A, 404, 414, 414G, 500A, 503, 600, 603, 604, 620, 620E31, 625, 626, 628, 629, 630, 630E, 635, 636, 638, 639, 640E, 645, 646, 648 & 649.
Price includes shipping, return for refund if fails on your Singer restoration.