For piecing, I use whatever I can find that needs used up and matches colorwise. I may have to adjust the needle position to accommodate a thicker thread, but that is no issue. The kind of thread is no issue either, cotton or poly. My machine sews equally good with anything I put on the top or bobbin for piecing. Now.....fmq is an animal of a different color! My machine does much better with a finer poly thread for fmq....the tension is easier to keep at a good place. I guess my point is that for piecing, there is no right or wrong thread. Poly thread is fine, contrary to what the quilt police may tell you. If the thread passes the breakage test, then it will work for me!