These are the ink cartridges we use in house when assembling our TiClicker®, TiButton® and NottaBolt® pens. There are other brands and options out there, but if you're like us, and like what came with your pen, we made this your one stop shop!

Ink Cartridge options: 

Our OEM Schmidt cartridge, Schmidt EasyFlow 9000M. Available in black or blue ink.
Our OEM Pilot G2 Mini cartridge, available in black or blue ink.
Our OEM Pilot G2 Full Size cartridge, available in .5mm & .7mm, both in black ink.

Newly added is the:
Monteverde Capless Ceramic Gel to fit a Parker size pen in .5mm, in black ink. 
Schmidt DSM 2007 for our LeadSlinger® (Mechanical Pencil) in .5mm and .7mm