Fil-Tech Magna-Glide Poly Classics Style M Jumbo 230yd Prewound Bobbins 100ct White . No. 60 Filament Polyester . Fil-Tec Bobbin central's patented magnetic core creates consistent delivery through the entire bobbin. No more interruptions for tension adjustments as your bobbin gets smaller. Magnetic core prevents backlash or over-spin and eliminates the need for backlash springs. Magna-Glide is the original high-yield magnetic-core bobbins. 100 bobbins in box. CHK-12445-M