I piece with 50 weight, generally Aurifil. My favorite machine quilting thread is Coats & Clark machine quilting thread 30 weight which is a cotton thread. I've never had breakage with it and it is economical. Another plus is that one of the places it is sold is Walmart which is a few miles from my home as opposed to a quilt shop or JoAnn's which is 30 miles away so if I run short it's not a problem. My Janome machine does not like Coats & Clark Dual Duty thread in the top. I can use it in the bobbin and so have been using up my odds and ends that way.