I had a bobbin case that would not stay on the machine no matter what bobbin I put in it. It turns out someone had put a little plastic ring in there and it made the bobbins stick out too far. I've had bobbins that had burrs on them - brand new bobbins with burrs. I've seen rusty bobbins. I've seen bent bobbins. Worn plastic bobbins. I would not toss out all old bobbins with out looking them over to be sure they are ok. They just aren't making them like they used to.