S and Z Twist Explained
Recently, there has been a lot of talk about S twist and Z twist threads. Some refer to the twist as a left or right twist, but the proper terminology is S or Z twist. Thread is made up of multiple strands, usually two or three strands (also referred to as "plies" or "ply") twisted together, although some may have as many as six or eight strands twisted together. All sewing, embroidery, or quilting threads made for home machines, industrial machines, or longarm machines should have a final Z twist pattern.
The initial twist (or first twist) for the individual strands should be an S twist. These strands are then twisted together in a final Z twist to form the thread. This is the same worldwide for any major brand of sewing, embroidery, or quilting machine. There are a few threads that have the opposite twist. Some hand quilting thread, knitting, and weaving threads have a final S twist. If you use a thread with an opposite twist, the thread will loosen instead of tighten as you sew with it. Threads are not marked with the twist pattern because it isn't considered essential to know. If you use quality thread from a reliable company and manufactured in a reliable country, and use it for its intended purpose, most likely it has the proper twist. If you notice that your thread unravels as it sews, it is probably a thread not intended for machine work.