Fly tying bobbins are an essential tool of the fly tier. The bobbin holds your thread spool and maintains constant tension on the thread, helping you to make durable, proportional flies. We offer two bobbin designs. The most common type of bobbin is the spring bobbin. Tension is applied to the thread spool by squeezing the spring arms together to increase tension or spreading the arms apart to decrease thread tension. The Chase bobbin uses a screw to increase and decrease thread tension.