The blood knot is the one associated with joining lines of similar diameter. It is built from two opposing wraps, so the two lines meet in a slim, symmetrical join. That is what makes it a leader and tippet knot: when the two sections are close in diameter, the knot draws down evenly and passes through the guides cleanly.

• A. Arbor knot
• B. Whip finish
• C. Hook keeper
• D. Blood knot

Answer: D. The other three options are not joins between two lines at all. The arbor knot anchors backing to the reel arbor; the whip finish is a tying finish that locks thread; a hook keeper is a fitting on the rod, not a knot.

Use the blood knot when the diameters are close. When they are very different — backing to fly line, for example — the wraps cannot draw down evenly, and the Albright is the better-known answer. On the water, the blood knot’s slim profile is why it is trusted at the leader-to-tippet join, where the knot has to pass through the guides.

Source

From Animated Knots: blood knot; terms follow the FFI Fly Casting Definitions.