The Blood Knot is good for building leaders where line of similar diameter and material are to be joined. The blood knot is one of the best for producing a leader with droppers. When creating droppers remember to allow extra length in the tag end for the dropper. Also remember that the dropper should be made from the tag end of the strongest length of standing line used to form the knot. The knot should be tightened by pulling slowly on both standing line lengths. The tag ends should be pulled slightly at stages so as to avoid unwanted loops or bunching in the knot. If you need to join leader material of significantly different thicknesses you should use a knot like the Albright knot.