123m x 144 bobbins per box Smooth, fine, practical and ready to use Magnetic side pre-wound embroidery bobbins. The only bobbin that is specifically designed to sew without tension variation throughout the entire bobbin. The magnetic sides are designed to create consistent tension from beginning to end of each bobbin. Pre-wound bobbins are practical, always ready to use and have the same amount of thread on each bobbin, which means all bobbins can be changed at the same time without wastage.