One of the many subsections that fall under the umbrella of woodturning, is the discipline of "penturning".
This rabbit hole, is a particularly deep one. However one that I hope I will demistify.
Firstly, for each pen model there is a corrosponding bushing and drill bit size!
(dont worry, I will explain certain terminology as I go)
Bushings slide on the pen Mandrill, normally on either side of the pen blank, allowing the blank to be turned to the correct size for the pen kit being turned, the centre bore is of a standard diameter, from what i have seen so far. Please let me know if this is not the case.
A Mandrill is an adjustable shaft, that can be locked to the correct length for the barrel of pen, whether that may be a single or double barreled, depending on the design and model of pen or pencil being turned. A point worth noting, please check the taper that your lathe accepts, The Record Power DML250 (My Current Lathe) takes a 2 morse taper
This picture shows the relation between the pen kit,, bushings and the mandrill.
Pen turning blanks (the white cylinders) are turned to marry the outside diameter of the corrosponding pen kits bushing. Well strictly speaking only the ends of the blanks need to marry the bushings (to ensure a seamless transition from blank to pen kit furniture) inbetween is upto your artistic inclination. I suppose the only guilding factor is the need for the finished pen to be comfortable to be held.
Next Week I will go through my process of turning a pen. If you have any questions, please leave me a comment below and I will endevour to answer the best I can.