Fil-Tec Magna-Glide Bobbins are known as the "high-yield bobbin without tension variation." High-tenacity, polyester filament thread is wound onto a magnetic core to give you consistent thread delivery throughout the entire bobbin. Gunold stocks Fil-Tec Bobbins in style "L" (135 yds.) pre-wound with black or white thread, or style "M" (230 yds.), pre-wound with white thread. Sold in boxes of 100.