We stock private reserve fountain pen ink cartridges for handmade pens. Most handcrafted fountain pens (whether made by Trobee or not) use standard “International size” cartridge refills unless otherwise noted. To change fountain pen ink cartridges simply unscrew the nib section of your pen and twist off the ink cartridge. Take the new cartridge and press it onto the nib unit until it is firmly seated. Gently write on a scrap of paper until the ink begins to flow.