From the manufacturer:
Pitt Artist Pen Dual Markers feature a smooth, flexible brush nib for artistic work and a metal-encased 0.8mm fiber-tip for adding detail. The thick brush nib is suitable for fine to thick lines and allows for vast coverage, the fiber-tip for fine drawing, contours, lettering and accents.
The finest India ink in a practical drawing pen: the water-based ink is highly pigmented with excellent lightfastness. It is odorless, permanent, waterproof and the ink will not bleed through paper. The transparent colors are buildable and perfect for layering. Ideal for mixed media techniques!