Graphite/Vespel ferrules are 15% graphite and 85% polyimide. They are the best choice for glass columns and polyimide-coated, fused-silica capillary columns and can usually be removed easily from columns. Quantity: Package of 10 Nut Size: 1/16 inch Column Inner Diameter: 0.32 mm Ferrule Inner Diameter: 0.4 mm