The famous Rotring Rapidograph is a precision ink pen, notable for its refillable cartridge system. Rotring offers fifteen nibs of different sizes, made of stainless steel. Rapidograph pens work on tracing paper, vellum and lineboard, as well as a range of drawing surfaces.
The advantage of Rotring's pens is that they deliver a line of consistently equal weight; there are no areas where lines are thicker or where the ink bleeds away. Newer Rotring pens offer a pressure-equalization system where each ink cartridge replaces the "ink helix." Older pens had an ink helix that required careful and complicated cleaning.
Isograph pens, like Rapidographs are technical pens. However, Isographs do not use ink cartridges. Instead they have a refillable ink reservoir, so you use bottles of ink to refill the pen.
Rotring's ArtPens are calligraphic pens, available with stainless steel nibs in a variety of sizes. These are used mainly for calligraphic writing instead of drawing, though many fine artists appreciate the varying line widths produced by Rotring's ArtPens.
Rapid Pro is one of Rotring's mechanical pencil lines, made for technical drawing. The entire pencil is made of stainless steel, and the barrel is hexagonal and has a knurled area near the tip that helps steady the draftsman's grip.
Rotring's Tikky instruments are more for everyday use, and the name "Tikky" describes pens, mechanical pencils and a three-in-one multipen. The Tikky pens and pencils are cheaper, and the pens are eventually disposable as users cannot refill the ink in Tikky pens.