I know there are thread "purests" out there, but I use serger thread all the time in my bobbin, YES, even for sewing my pieces together. I'm not making heirloom quilts. I once read an article that said not to use thread that is soooo strong it won't break. WHY you ask? Well it's easier to repair a seam that's opened up than repair a block that's torn because the thread wouldn't give. Makes sense to me.