pen
thingiverse
These are just the plastic components, but you'll also need a spring and additional materials found in another pen to complete the job. Good luck with that.
Download Model from thingiverse
With this file you will be able to print pen with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on pen.