The thread ply is important as well as the wt. to know what size needle to use. A 50wt 2 ply is much thinner then a 50wt 3 ply and each needs a different needle size. It's very important to keep a notebook of what thread and needle works for each application. Most thread issues when sewing is due to lack of information about the thread itself. Superior offers detail info about what needle size to use with each of their threads. Once you have experience sewing with the right thread and needle it will be easy to know exactly what is causing your thread problems.