Originally Posted by k9dancer
Older machines do not have an automatic bobbin stop, so it is possible to overfill those bobbins. That thread just goes to waste if you have to pull it off to get the bobbin in the case, so I'd rather have my bobbin a little under than over. That said, I get as much thread as I can comfortably fit on my bobbin, and I load up about 20 of them before I start.
True - I learned to sew on an old Singer and it was possible to overfill bobbins if you were not paying attention, and it caused problems.