Bulb frosted like the 649 bulb
Singer 99K, 201, 237, 328, 401, 630, 717, 935, 1200, 2000, 2210, 4011, 4552, 4610, 4617, 4622, 4623, 4830, 4832, 6136, 6212, 6233, 6267, 6268, 6704, 6705, 7000, 7004, 7005, 7028, 7050, 9005, 9008, 9010, 9134, also Pfaff serger 4762, round double contacts