Invert the fly in the vice. Take some hackle fibres and introduce them to where they will be tied in. Perform two wraps of thread around the hackle fibre stems and let the bobbin hang loose. Now adjust the hackle fibres until you are happy with their position, then take the bobbin again keeping the thread taught and secure the hackle fibres in with thread. Now invert the fly again in the vice so that it is the correct way up and trim any waste ends that are protruding.