When tied correctly, the blood knot has a slim profile that passes through the rod guides nicely. It is one of the best knots to use when splicing lines that are similar in diameter (40-pound to 30-pound; 30-pound to 20-pound, etc.). Another noteworthy quality of this knot is that the two sections of the leader it connects fall in a straight line with each other creating a more natural taper, which is the ultimate goal in leader construction. Because of this characteristic, the blood knot is one of the more common knots used in any tapered portion of the leader. This knot should not be used when connecting lighter sections of the leader to heavier sections, such as a class tippet to a bite tippet (20-pound to 80-pound); however, in some cases you can do so by using an improved blood knot. The improved blood knot is tied the exact same way as a blood knot is except that the lighter leader material is doubled.
Tying Difficulty: Moderate
Breaking Strength: Approximately 85-95%
Tying Hint: Leave yourself plenty of tag on each separate piece of monofilament; it will keep the knot nice and neat prior to cinching.