Answer Sue, You will find wool needlepoint thread comes in 3 types: Crewel, Persian, and Tapestry. Crewel wool is a single strand that is used on smaller gauge canvas. Crewel can be doubled or tripled for use on larger gauge canvas. Persian wool is three strands twisted together. Most often, Persian threads are separated, and two strands are used on medium gauge canvas. Single strands of Persian can be used like crewel threads, as well as all three strands being used for larger gauge canvas. As an aside, Persian wool is not necessarily from Persia (known as Iran today); it’s just the name used to describe the three-strand lay of the thread. Tapestry wool is not stranded. It is a thicker yarn than Crewel or Persian. It is used for medium to larger gauge canvases. Unless the canvas gauge of your stocking is very large, I would recommend Persian wool, as it is the most versatile; you can use one, two, or all three strands (or more) of the Persian wool to cover any gauge canvas.