I have two Singer 66's and as I was readying one to get the treadle all ready for use, I spotted the same thing and tried to pull that piece of red fuzz out of there only to think that some goblin was down there hanging on to the other end. When I let go of it, it boinged back, somewhat, and that is when I realized that it was a spring. I had not been able to find my replacement manuals I had downloaded from the web since I moved, but now made a concerted effort to find them. Sure enough, in my clothes closet, found the binder with them and found out that I had been trying to remove what wasn't supposed to come out. We shall see what happens when I get the new belt on, the treadle area cleaned up and try to sew. So, Vintage ladies, if you see a bit of red fuzz just to the right of your bobbin case, DO NOT TRY TO REMOVE.