Choose the head that fits around the eye without touching the wing or the hackle fibers. The thread loop is formed on the tapered section and then slid toward the fly while under tension. The tool is used for intermediate ties as well as for finishing the fly. Choosing the correct diameter prevents a cone that is too wide from coming into contact with a small, already-tied head. The set includes 1.5, 2.2, and 3 mm heads.