The Montana Sketch Liners are ideal for precise lines and detailed work. The ink is photocopy-safe and waterproof. These pens come with the AP-Mark quality seal, ensuring a pure black colour. The nib is constructed of a durable synthetic material that will not break or fringe. The Montana Acrylic series is also compatible with the markers. Other sizes are also available. Montana Sketchliner Pen Pen Set (5 Pack) Perfect For Fine Detailed Work and Lines Ink Is Waterproof and Photocopy Safe Certified With The AP-Mark Quality Seal Guarantee A True Black Colour Nib Is Made Out Of Strong Synthetic Compatible with The Montana Acrylic Range Different Sizes Also Available Description by: Vik