Bead wire refers to a flexible wire with a nylon coating. Common brands are Soft Flex, Acculon, etc. They come in a variety of diameters, which refers not only to how thick the wire is, but its strength. Soft Flex is actually marked as superfine, fine, medium and heavy to make it easier. Choose your wire size based upon the weight and size of your project. If you are using very fine beads with small holes, think about using a fine or superfine diameter. If you are using big chunky beads, or hanging a heavy pendant on your piece, think about using a heavier bead wire. Remember, you will have to go through the end beads twice to attach a crimp bead so check out the hole size and plan accordingly.