The thorax version of many dry flies is designed to make the wing the most predominant feature of the fly and to support the fly at a different balance point, offering a slightly different profile to picky trout. If standard dries are not doing the job, it is often worthwhile switching to a thorax design as a change-up. Color, Blue Winged Olive.Dry flies in sizes: 16, 18, 20, 22, 24.