30 and 40 Weight - Weight refers to a thread's thickness. With embroidery thread, a lower weight means a thicker thread. Specifically, our 30 Weight embroidery thread is heavier than our 40 Weight thread.
40 Weight thread is more popular because it can be used to embroider both small areas (e.g. a Polo logo) and larger areas (e.g. numbers on a football jersey). 30 Weight thread is often a better choice for large areas. It covers them faster with less stitches because it is thicker, and it is indistinguishable from 40 Weight thread. Using 30 Weight thread requires a larger needle and more machine tension.