Technical Fountain Pens
The technical fountain pen (or Rapidograph pen) is generally used for ruling straight lines with the aid of a T square, triangle, or other straightedge. It may also be used for freehand lettering and drawing. One of the best features of the technical fountain pen is its ink reservoir. A standard set of pens 11 line sizes, ranging from 000, the finest, to 8.  Some pens are labeled by the metric system by the line weight they make. Other pens are labeled with a code that indicates line width measured in inches. Most technical fountain pens are color-coded for easy identification of pen size. These pens are available either as individual fountain pen units, resembling a typical fountain pen, or as a set, having a common handle and interchangeable pen units.

Graphos Set

Kohi Noor Tech Pen Set

Faber Castell Tech Pen Set

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Each pen is composed of (see drawing below):

• Cap
  
  
• Feed and  Point Module
  
  
  • Body,
    
    
  • Point and Feed Tube, and
    
    
  • Cleaning Pen and Retaining Cap
    
    
• Ink Reservoir
  
  
• Color Ring and Clamp
  
  
• Holder (or Barrel)

The Feed and Point module is the heart of the technical fountain pen and consists of the Feed Tube, Cleaning Pin, Retaining Cap, and Body. It controls ink flow and defines the drawn line. The Feed Tube holds the cleaning pin, which is very delicate and mounted to a plastic or metal body. Inserting the cleaning pin into the feed tube after cleaning is where the majority of problems develop with this kind of pen, especially in .35 size and smaller. The combination of point diameter and gauge of the cleaning pin determines the line width. In function, the cleaning pin acts as a valve, protruding beyond the edge of the bottom tube when the pen is not touching the drawing surface. Ostensibly when in this position no ink flows. When the pen is resting on a drawing surface, the cleaning pin is pushed up, allowing a flow of ink. Action of the pin in the point tube is intended to minimizes ink clogging. For information about the care and cleaning of these pens see Care & Cleaning of Technical Fountain Pens.

The design of the Reservoir depends on the design and vintage of the pen. It may be a part of the Feed and Point module or is a removable translucent plastic ink cartridge that attaches to the module. The large ink capacity of the reservoir saves time, i.e., no constant replenishment of ink to tip.

Technical fountain pens have replaced older designs in preparing drawings and diagrams. Adaptors also have been developed to allow use of these pens for mechanical and template lettering (see associated articles). The adaptors hold the Feed and Point Module of the pen with reservoir attached, and are available for Leroy scribers or in pivot form for template lettering.