Tube flies are exactly what they sound like.... They are tied up on a tube instead of a standard hook shank. Tubes are thicker than a conventional fly, an attribute most steelhead and salmon fishermen find desirable. Hook size and style can be varied for whatever situation you are fishing. Single, double and even treble hooks (regulations permitting) are all possibilities. Since the hooks are not part of the fly there is no chance of the hook rusting before the fly has seen its end. There are also more hook-ups with tubes. With the fly and the hook being separate, when you set that hook the leverage of having a long shanked fly is eliminated. Of course this helps you hold on to more fish after hook-up as well.