Threads and wires are important materials used in fly tying to secure materials to the hook shank, create a smooth body, and add weight and flash to a fly pattern.
Threads are used to tie down materials to the hook shank and to create a smooth and even body on the fly. They are available in a range of colors and thicknesses, allowing fly tyers to match the color and size of the thread to the fly pattern being tied. Some common types of threads include 6/0, 8/0, and 12/0, with the number indicating the thickness of the thread.
Wires are used to add weight and flash to a fly pattern, as well as to reinforce certain parts of the fly. Wires are available in a range of thicknesses and colors, and can be used to create ribbing on a fly, wrap around the hook shank to add weight, or as a body material on certain types of nymphs and streamers.