Here's my confession. My (vintage) machine came with metal bobbins - the kind with four holes in the sides, three large holes and one smaller hole next to the middle that, I assumed, was for putting the thread through prior to winding. One day I was trying to thread it and getting a little frustrated since that little hole is so far from the edge it is hard to hit, when the light went on. Why was I going for the small, far away hole when the larger, closer holes would work just as well? I mean, when the bobbin starts to wind, the thread still wraps around the center - no matter which hole I use, right? I gave myself a dope-slap and have never bothered with that little hole again.
Tate