Materials – resins, ebonites, acrylics.
How thin or thick? How long? Size and what my pens look like next to more familiar brands.
Nibs. Not least important is the writing tip.
Section Shapes – How do you like to grip your pen?
Filling – How will you fill your pen with ink?
Steps? – That little shoulder on the barrel is called a step. Will it fit your hand?
Clips & Roll Stops – Steel and custom options.
Rings and Bands – want to add some spice to your design?
Ink Windows – Do you need to see how much ink is left?
Vent Hole in Cap? – Regulate that air pressure.