I have a Viking Sapphire, too. During the owner's classes, the ladies said over and over never to use Coats and Clark, but one of my classmates did and it wound around the presser foot from the top and bobbin thread and broke the foot in half - no joke, it broke an acrylic foot in half!! Needless to say, I never tried Coats and Clark. I usually use Guterman and I only have regular, user error issues.