Question: what is the difference between 40 wt and 50 wt thread?
Answer: Machine quilting Because the 40 weight cotton thread is heavier than the finer 50 weight cotton thread, quilting stitches will show up more easily on the quilt. While the 40 weight cotton is heavier than the thread you'll want to use for piecing, it is still thin enough to easily be used in home sewing machines.