From the web sites, it appears TEX is the shortened name for textured. It refers to strength. The faster a machine operates and the needed tension on the thread to get a reliable stitch affect how much TEX is needed in a thread to work on a given machine. The way my Gammill is set it needs 28 TEX minimum. When I shop for cone thread, I'm looking for that number. I've noticed that more companies are listing TEX on the label....sure helps.