invisible thread broke my machine!
I was using this thread so it would be quicker to remove it when the muslin was washed. All of a sudden it exploded....the bobbin fell out, minus the tension screw, which I did find. Then when I looked inside I found that the finger was not where it should be...in the place on the under side of the throat plate. It had broken off. The good part is that it has been replaced and working. The guy that fixed it said I should never use it........too strong. It had somehow sprung and wrapped it self around the bobbin mechanism and .......wham! This is my Singer 301, old, but great