Thread is useful for seed bead weaving or stringing very light beads. Thread comes in sizes designated by letter, not numbers as with beads. B is the most common size and comes in the most colors. It is useful for almost any bead weaving project. The reason to use thinner thread (Size A is thinner, Size O even thinner and Size OO the thinnest) is if you are passing through very tiny beads many times. B is suitable for most stitches with size 11 beads. The reason to use thicker thread (size D) is if your project is very heavy or you are sewing through leather or buckskin. D will not go through size 11 beads more than 3 times. If you are having a problem with fraying, you may wish to apply beeswax to the thread.
If your project is very heavy, consider using Fireline instead of thread (Nymo or Sylamide). Fireline feels like thread but is made partially with metal. It was invented by the fishing industry and is designated by weight (i.e. how heavy is the fish you are trying to catch – 4 lb., 6 lb., 8 lb., etc.) Most beading projects don’t require more than the 4 lb., but think about how heavy the project is before using it. The advantage is that Fireline doesn’t stretch out and thread eventually will. The disadvantages are that it costs a little more, only comes in two colors and once you knot it – it can’t be undone. We definitely recommend Fireline for the warp threads (the up/down) on a bead loom so there is no stretch. You can then use thread for the weaving part.