Abstract: Fine lines, for example, 0.5 to 0.8 mm wide, can be produced by the use of an auxiliary nib unit which fits over a main nib on a felt or Fiber tip marker or on a technical pen. The auxiliary nib is a friction fit in its housing. The marker cap may contain a receptacle for storage of the auxiliary nib. The auxiliary nib is movable axially of its housing so as to come into ink-transfer contact with the main nib irrespective of wear or distortion of the latter. The main nib may be of fibrous material, and the auxiliary nib may be a hollow extrudate of plastics material.