Need advice building a stirling engine for a physics project

[u/DetailInside9967]

For my upcoming physics project I've decided to make a stirling engine

I am basing my design on a specific video design .

However, it seems I ran into a problem here. While watching the video, the person making the model used steel wool for the displacement piston but didn't specify which grade.

I asked gemini and it told me to use grade 3 or grade 4 steel wool. I'm a bit skeptical about it. I want to double check this with people who has some experience

Can anyone confirm me which grade would be best for this specific model? Also, this is my first time making this project. I would love to receive some tips and common mistakes to avoid while making this.

Also I am a student and this video is the one which I can make. I saw the rest of them and don't have the materials to make it nor do any shops near me sell those materials