It is used to see the PLA scrolling.
All you need is a 2.5mm M3 screw to screw directly onto the shell.
Use the flexibility of PLA to rest on the wheel.

Filettata is for use with PTFE holder

Here you can see how it works: https://www.youtube.com/watch?v=Y9Vn8PPwJfs

Filettata: https://youtube.com/shorts/aI5Zd37TZDM?feature=share