I have used the Mettler 60wt. and 50wt. The 60wt. is really fine and disappears nicely. I was always frustrated with not having the right colors (I was always taught to match the thread to the applique piece) and the thought of having to buy 30 spools of thread for one quilt, of which I might only use a yard or two of, well I couldn't afford it. When I discovered the Masterpiece donut with 36 bobbins of different colored 60wt. fine cotton thread, I was so excited. If all your applique is being done with just a few fabrics, then buying full size spools of thread may make sense, buy if you are doing lots of colors, the donut is wonderful. I have always used just one strand, I have never heard of using two, it would be hard to make 2 disappear and not show.