Originally Posted by mtspools
I have head if you use it in the wrong place on your sewing machine it can wreck it. Can't remember if its the bobbin or upper thread.
I took a class in doing perfect circles using it in both bobbin and top with no problems. At the class, we used high-end Brothers, but it works on my Kenmore/Janome too. The invisible threads have come a long way from the old kind that looked like fishing line!