I normally use Coats & Clark All Purpose or Dual Duty thread for piecing which is supposed to be 50 weight but seems more like 60 weight. For quilting I've used the same, serger thread which is definitely less than 50 weight, Maxi-Lock Swirls--50 or 60 weight equivalent, Coats & Clark Machine Quilting thread 50 weight, Robinson Anton Cotton machine quilting thread 50 weight, and Sulky Blendables 30 weight. I have a couple spools of King Tut 40 weight but I haven't used them yet. I loved the Sulky Blendables but they're expensive and the King Tut seems very similar. I have also used Superior Signature for piecing & machine quilting because someone gave me a gift set of neutrals and I didn't have anything else handy at the time. It is also very nice, 50 weight I believe.