I was super frustrated with how quickly my Wacom nibs wore down and found this solution online. I gave it a go myself and it was so great I wanted to share it!
I didnt include this in the tutorial, and now looking back I probably should have. Someone on here who will remain nameless ( <3 ) told me that they had somehow managed to get their home-mad nip stuck in their pen. I visited them to have a go at getting it out (well okay...I visited them because they make good food and checked the nib while I was there...) and turns out they had purchased the snipper cord that was STAR SHAPED and not ROUND.
NO NOT use the star shaped cord. Make sure that the cord you buy is a smooth round tube. Even with the correct size the star shaped cord will make it just that little bit too snug in your pen and if its a tiny bit too short it will get stuck.
If for some reason you have also done this use a fine sewing needle to remove the cord from inside your pen
TL;DR USE THE ROUND CORD NOT THE STAR SHAPED CORD.