Manual sewing of buttonholes. Sewing buttonholes of different lengths. Gathering using thread or elastic thread (smocking). With or without cording. For 9 mm machines. Use this foot to make the tiniest of buttonholes or stitch one as long as needed, even one large enough for a pocket opening #3 works with 5.5 mm and 9 mm machines. #3C works with 9 mm machines Compatibility. B 570 QE/QEE, B 590, B 710, B 740, B 750 QE, B 770 QE/QEE, B 790, B 790 PLUS, B 780, B 830, B 880, B 880 PLUS. Get more info.