i use connecting threads cotton 40wt for piecing and have never had a problem. i also use it to fmq on my brother with no problem. right now i'm using a 50wt prewound bobbin (who knows who made the thread?) and my usual 40wt top thread. my brother sews with anything and never has had a problem so perhaps that makes it a less than strong endorsement for the thread. i have never had a picky machine, knock wood! lol. even the metallic thread gets along well, no special care taken or needed. (so far). i do really like the connecting threads thread for the colors, strength and nice stitches. hope you find a thread that you and your machine agree upon. 8-)
