The 8mm Slimline Pro kit comes in both click pen and click pencil versions. Two tubes are required per kit.
https://www.pennstateind.com/store/PKPENXXCH.html
https://www.pennstateind.com/store/PKPCLXXCH.html
For additional information consult the penmaker's interest group in the Shapeways forum:
https://www.shapeways.com/forum/t/penmakers-and-3d-print-pen-making.80076/
Extra notes: This blank section is experimental. The idea is to glue two of these sections made of different materials to the brass tube to end up with a pen having two different colors. Once glued together the blank must be machined to remove excess material.