100 BLACK bobbins per box130 yards per bobbin. Fil-Tec Magna-Glide Classic Pre-wound Bobbins L Style 67x2 High-Tenacity Polyester Filament 60wt, Tex 12. The patented magnetic core creates consistent delivery throughout the entire bobbin. No more interruptions for tension adjustments as your bobbin gets smaller. Magnetic core prevents backlash or overspin and eliminates the need for backlash springs. Magna-Glide is the original high-yield magnetic core bobbin.