. Each BERNINA sewing machine has a special hook for bobbins and bobbin cases. Different bobbin cases are therefore available, depending on the machine. The CB Hook is used in particular for sewing utility and decorative stitches with a stitch width of up to 5.5 mm CB-hook Bobbins and Bobbin Cases are required for the following machines: For all BERNINA activa and 3 Series machines. BERNINA virtuosa. BERNINA aurora. BERNINA artista 165, 170 and 630. BERNINA 555 and 570