5/7 Blood Knot
I think the Blood Knot was so named because most people sweat blood when trying to tie it. Actually this knot isn’t hard to learn, and it’s a great connection between pieces of mono. The Blood Knot is thinner in diameter than a Surgeon’s Knot and hangs up less in weeds. But if there’s more than 0.002 inch difference between the two pieces of material being joined, then the standard Blood Knot, made with five turns on each side, doesn’t pull up correctly
When I began extensive experiment with leader materials and leader designs in the early 1970s, I discovered that if the two pieces of mono differ by more than .002 inch in diameter, and if 5 turns are taken with each sized material, the smaller-diameter material pulls tight first. Once that happens, the heavier material can’t side tight, and the knot can potentially unravel. From these observations, I developed the Double Blood Knot to tie together pieces of mono having more than .002 inch difference in diameter (see my book, “Nymphing,” 1979). In the mid 1980s, I discovered a better way to tie the Blood Knot that is faster and produces a more balanced knot.
It’s called the 5/7 Blood Knot. Instead of making 5 turns with each end of the material, the angler ties the knot using 5 turns with the heavy material and 7 turns with the light material. For example, when joining 0.020 inch to 0.014 inch, make 5 turns with the 0.020 and 7 turns with the 0.014. The extra turns with the lighter material produces a knot that pulls up evenly; each side slides tight at the same rate and the knot forms perfectly. It’s the same length from the center of the knot to either end.
5 turns with the heavier material and 7 with the lighter material balances the knot correctly. Drawing by Jason Borger