Those screws are for holding the feet attachments on your presser bar, and mounting the binders on your machine.
The cap of this screw is thicker than normal screw,it will help you screw it easier.
They will fit most sewing machines like SINGER, JUKI BERNINA, PFAFF, JANOME, KENMORE, VIKING HUSQVARNA , BABY LOCK etc
They would also fit and hold vintage SINGER sewing machine Face plates & Back Plates