Permanent fineliner black ink pens flow evenly for arts, crafts, sketching and drawing. Acid-free, archival quality, fade resistant, indelible pigment ink is lightfast and waterproof. Erasable when used on drawing film. Won't bleed when highlighted. Long metal tips are ideal for use with rulers and templates. Include sturdy metal clips. Pens can be left uncapped for 18 hours without drying out. Set of four pens includes one each 0.1mm, 0.3mm, 0.5mm and 0.7mm line widths. Nonrefillable.