thickness to a traditional HB (US#2) pencil lead. Pigments Mechanical pencils with colored leads are less common, but do exist. Crayola's "Twistable" product line includes two different types of colored pencils (erasable and non-erasable) with mechanical feed mechanisms, but does not offer refill leads. Several companies such as Pentel, Pilot, and Uni-ball (Mitsubishi Pencil Co.) currently manufacture colored refill leads in a limited range of diameters (0.5 mm, 0.7 mm, or 2.0 mm) for their own products. Koh-i-Noor makes mechanical colored pencils with replaceable leads in 2.0, 3.15 and 5.6 mm sizes. See also Technical drawing tools Notes and references Bibliography Deborah Crosby, Victorian Pencils: Tools to Jewels, Schiffer Publishing Ltd., Atglen, PA, 1998 Jonathan A. Veley, "The Catalogue of American Mechanical Pencils", Greyden Press, 2011 External links Sharp's history of the mechanical pencil History and development of Keeran's and Hayakawa's pencil styles Leadholder Museum (History and Images of Leadholders) Sampson Mordan. First patent for a mechanical pencil Inventor never got rewards of pencil business - Pantagraph (Bloomington, Illinois newspaper) Pencils Writing implements