Magna-Glide White Continuous Filament Polyester Bobbins Style M. Magna-Glide bobbins are specifically-designed for metal bobbin cases used in commercial embroidery applications. Magnetic core offers uniform tension control throughout the entire bobbin – no more throwing away partially-used bobbins due to erratic tensions! Magna-Glide bobbins have no (or very little) lint buildup, and no overspin or backlash concerns. 230 yards per bobbin, 100 bobbins per box. White Continuous Filament Polyester, Style M.