Page 39 - Joseph B. Healy "The Pocket Guide to Fishing Knots"

Blood Knot

This is an elegant, utilitarian knot, often preferred by anglers for joining
sections of a leader.

1. Cross two strands of monofilament so you form an X. Give yourself
a break and leave about six inches of tags at the top of the X. Now
“walk” the tag ends up the standing end, left and right. You’ll have to
focus, using some dexterity to wrap the tag ends. Use your thumb

and forefinger, if needed.
2. Use seven turns for light material, five turns for regular-diameter
material, and three turns for heavy stuff. After you make these turns,
thread the tag ends through the loop at the X. Again, you’ll need
some dexterity with your fingers to do this with both tag ends.