At the center of a pen is the ink-delivery system. For the common ballpoint pen, this system is a long cylinder that runs the length of the pen and has the ballpoint tip at the end. A fountain pen uses a similar system, but the tip is installed on the pen itself. Disposable ink-delivery systems are found in inexpensive ballpoint pens. Refillable ink cartridges are found in the more expensive ballpoint pens and fountain pens. According to Penspotters, the most common kind of ink delivery in pens today is the cartridge system.
Calligraphy pens and fountain pens have removable tips. You can replace a worn-out tip, or you can change the style of the tip to get a different result on the page. Ballpoint pens do not offer a removable tip.
The feed is the part between the tip and the ink-delivery system that helps to regulate the flow of the ink. Without the feed mechanism, the ink would spill out of the tip and onto the paper uncontrollably.
The barrel is the extended portion of the pen that you grab on to when you write. In some cases, the barrel is contoured to make it more comfortable to use. You can also buy barrel pads to add a cushion for your fingers.
The point at which the tip of the pen meets the barrel is referred to as the section. The section is normally a threaded connection that can also have external threads for the pen cap.
The mechanism is the way in which the tip is revealed. In some cases, such as a fountain pen, there may not be a mechanism because the tip is already extended and covered by a cap. Ballpoint pens are best known for having a mechanism that is usually a button that can be pressed at the back end of the pen to reveal the tip. Another variety of mechanism is a twist mechanism where the barrel must be twisted to reveal the tip.