Uses: The Blood Knot is a favorite knot for fly fisherman. It is primarily used to join two lines of similar size, e.g., when joining sections of leader or tippet, and is one of the best knots for this purpose. The strength of the Blood Knot depends on making at least five, and up to seven, turns on each side of the center
Pulling the Knot Tight: When lubricated and pulled tight, the Blood Knot changes its structure. Pulling on each line forces the wrapped turns to redistribute the twists so that the inner strand becomes an outer wrap (not illustrated in the animation using rope).
Tying it: There are several methods of tying it. The animation shows each half being created separately, which provides a good picture of the structure of the Blood Knot.
Alternative: An alternative method is to just overlap the two ends and twist them together for about ten to fourteen turns. Then go to the center of the twists and create a hole. Pass the two ends the opposite way through the hole.
Whichever method is used, the Blood Knot is usually symmetrical about the middle. Although the twists usually continue in the same direction either side of the center as shown in the animation, it can be tied so that the wraps are mirror images of each other.
Advantages: The Blood knot is a simple, easily learned and very effective way of joining two similar sized lines.