Koh-i-noor 4190 HB 2.0 mm Graphite Leads for Technical Drawing. Koh-I-Noor Hardtmuth Graphite Leads are made of the highest quality graphite. The smooth graphite is available in a variety of hardness ratings to give you dark lines and expressive strokes. The lead is of 2 mm diameter and suitable for use with mechanical clutch pencils. They can be easily refilled into the clutch pencils. They are ideal for use on newsprint, Bristol, colored paper or heavily textured surfaces. Depending on their hardness they are suitable for artistic work or technical drafting.