An XACTO blade pen thing, im not really sure what to call it, fits under a 9mm base-wide blade.
Initially threading the cap onto the pen may be difficult, it was for me, I recommend using two pliers to initially thread the cap and repeat until the cap is easily removed by hand. This difficulty is likely due to the resolution of my printer so you may have better luck then me.
Recommend high resolution for the threading.
Depending on print orientation support may be necessary.
If you are having trouble threading the cap onto the pen I recommend scaling up the cap by an additional 1-3% and try again
The issues at the end of the pen are due to my lack of support material.