Koh-I-Noor's technical pens are for general technical drawing use when you require a constant line width. The plastic body encases a stainless steel tip which screws into the main body of the pen and is removable for cleaning or replacement. A refillable clear ink cartridge is included with each pen. Ink sold separately. Pens should be cleaned on a regular basis so they won't clog. 3165 Series.