Hi there.
I have a Designer 1 USB which came with two felt discs - a small one, I assume for small cotton reels, and a larger one for large cotton reels.
My recollection is they were sitting on the machine, on the corresponding spools, when I opened the box eight years ago.
This morning, when I checked the User's Guide, I could find no specific mention of them, or what their purpose might be. I am assuming it is to keep the cotton reel steady as it feeds the thread through the sewing machine, and probably helps with stitch quality.
Hope that helps
Aussie.