The bend of the hook can be a matter of great debate concerning the hooking qualities of the various shapes and the fact that some are just a matter of eye appeal. The Viking, Limerick and Sproat are the three most popular and have been around for many years. They all fish well and more importantly hook fish with pretty much the same efficiency.
The gap on a certain hook, for instance a No. 6 will always remain the same but the length of the shank can be very short, like a 5 extra-short or especially long, such as an 8 extra-long.
Threads
The thread is used to attach the various materials to the shank of the hook. The basic required thread sizes are 3/0 (three ought) and 6/0. Here the higher the number the smaller the diameter of the thread. The 3/0 thread is rugged and great for the beginner as well as anyone else tying flies from the large 1/0 to the No. 12 & 14. Flies smaller than No. 14 will need a smaller diameter thread and that's where the 6/0 comes in to play. There are other threads and we will discuss them in detail but suffice it to say that these additional types are used to apply special material to the imitation that the 3/0 and 6/0 would be considered inappropriate.
Body Materials
These are the materials that are used to build up the imitation to give the elusion of thickness, shape and texture. These materials also will give the imitation a particular motion and this action must be purposeful by looking natural to the fish. Various animal furs and synthetic furs are in this category. Other materials would be Hackle stems or Latex and flat synthetics like Swannundaze.
Furs like Opossum, beaver, badger, mole, seal and rabbit are by far the most popular. Wool yarn, Chenille and the synthetic Antron are used as well since all these material will absorb water their use is primarily for Wet Flies and Streamer patterns. Once the body has been constructed the material must then be secured to the hook shank. Using the thread itself or another material such as does this: wire, tinsel, feather stems and peacock herls.
Hackles These are the individual barbs that come from a variety of birds. The most popular are the Hackles from the neck feathers of chickens. The Dry patterns use the Hackles from the neck and saddle area of a rooster chicken. Also because the saddle feathers tend to be very long, they are used for al sorts of streamers. The Hackles used for Wet flies come from the neck areas of either a No. 3 rooster or a hen. Hackles for the Dry fly need to be stiff, glossy and have no webbing between the barbs. Hackles for the Wet fly have to be a lot softer and have the webbing to absorb Water.
Wings and Tails
The most popular material for paired wings is the paired sections from the flight feathers of the mallard duck. Also used are the flight feathers (Quill) of the following: wood duck, teal, pintail, grouse, pheasant, turkey, deer hair, elk hair and various animal tail hair, such as, calf, bucktail, fox, squirrel and even the woodchuck. Flank feathers, located on the body of the bird at the base of the wings, are also used. Again, you need to use the correct material for the right reasons. If your fly needs to float than the feathers have to be stiff and the animal hair has to be hollow. If the imitation needs to sink then the feathers will be much softer and the animal material will be fur and not hair.