How to Tie the Blood Knot
By Alex Clayton · Updated 23 October 2026
The blood knot, also called the barrel knot, is a knot for joining two lines end to end. Each tag end is wrapped around the other line, then both are tucked back through the middle so they lock against each other.
Plenty of guides use the same name for a hook knot. That one is the half blood, or clinch. The full blood knot is effectively two half bloods tied around each other, and it only joins line to line.
Use it to build a tapered fly leader, to add a lighter length of line to a heavier one of similar diameter, or to make a dropper. It is slim, suits small, stiff or slippery line, and trims short. The catch: it is fiddly, and it works best when both lines are roughly the same thickness.
You need two line ends, a little water or saliva, and clippers. The steps below use 5 turns each side.
Step 1: Check the Diameters and Overlap the Ends
A blood knot can fail before the first turn: the lines are too different in thickness, or there is too little overlap to work with.
- Compare the two lines. The blood knot beds down best on lines of roughly equal diameter. If one is much thicker, tie a surgeon’s knot for joining lines of different diameters instead.
- Lay the ends alongside each other, pointing in opposite directions, overlapping by about 6 to 8cm (3in). Allow a little more on fine line or with cold fingers.
- Pinch the centre of the overlap between finger and thumb.
By now you should have a cross of line held at its centre, with a free tag end either side.
Step 2: Wrap the First Tag Around the Other Line
Five turns is a sound default for the blood knot.
Take one tag end and wrap it around the other line 5 times, working away from your pinched centre. Published instructions vary: some give 4 to 6 turns, others at least 5 and up to 7. If you are unsure, tie 5 and keep them neat.
Lay each turn beside the last rather than over it, because crossed turns stop the knot bedding down evenly. Count as you go, since you will match the number in Step 4.
By the end of this step you should have 5 even wraps, with the tag pointing back towards the centre.
Step 3: Bring the Tag Back Through the Centre Gap
This is where the wraps try to spring loose. The tuck locks the first half of the blood knot.
Bring the wrapped tag back towards the centre and pass it between the two lines where your wraps started, which is the crossing you have been pinching. Trap the tag in the same pinch so the turns cannot unwind.
The usual slip is tucking the tag on the wrong side of the crossing, or through one of the wraps instead of the centre gap.
By now half the knot is built, with a small opening left at the centre for the second tag.
Step 4: Wrap the Second Tag the Opposite Way
The second half mirrors the first: same number of turns, opposite direction.
Take the second tag end and wrap it around the first line 5 times, working away from the centre and turning it the opposite way to the first set.
Keep each turn snug as you go. Knot writer Stanley Barnes, cited on Wikipedia, describes two ways of coiling these turns, and notes that in fishing line one can change into the other as the knot tightens unless the turns are set snug.
By the end of this step you should have two matching sets of wraps either side of the centre gap, with the second tag pointing back towards the middle.
Step 5: Tuck the Second Tag Through the Same Gap
Get this tuck right and the knot is all but finished, with the option of a dropper thrown in.
Pass the second tag through the same centre gap as the first, but from the opposite side. Then check: one tag should point up and the other down, both in the same opening. If both entered from the same side, undo the second half and tuck again.
Leaving a dropper
Decide before you tighten. Leave one tag end long instead of trimming it, and that length becomes a short branch for a second fly or a small lure. Keep it long enough to tie a fly or hook on comfortably, and short enough that it does not wrap around the main line on the cast.
- Best for: fly anglers fishing a team of flies.
- Skip if: you only need a straight join between two lines.
By now the knot is fully formed but still loose, with both tags in place.
Step 6: Wet, Pull Tight, Trim and Test
A perfectly tied blood knot can still be spoiled here. Cinching it dry creates friction that can weaken monofilament and fluorocarbon at the knot.
- Wet the knot with water or saliva.
- Pull slowly and steadily on the two main lines, not the tags, so the wraps gather and bed down towards the centre.
- Trim both tags close, leaving a fraction rather than cutting flush.
Give the join a firm pull by hand before you fish. Retie if the wraps look crossed or bunched, one side slides, or the line is kinked at the knot.
You will often see a strength figure of around 80% quoted for the blood knot, but the only check that counts is pulling your own knot on your own line.
| Situation | Better choice |
|---|---|
| Lines very different in diameter, cold hands or failing light | Surgeon’s knot |
| Joining braid to mono | Double grinner knot, also called the double uni |
| Tying line to a hook or swivel | Improved clinch knot |
The blood knot is slimmer; the surgeon’s knot is faster. For other joins, see our full guide to fishing knots.
Frequently asked questions
Is a blood knot the same as a half blood knot?
No. The blood knot joins two lines end to end, while the half blood, or clinch, ties line to a hook or swivel. A full blood knot is effectively two half bloods tied around each other. For hooks and swivels, use the improved clinch knot.
Is the barrel knot the same as the blood knot?
Yes. Barrel knot and blood knot are two names for the same join, and the tying sequence in the steps above applies to both. The Ashley Book of Knots, quoted on Wikipedia, uses the name barrel knot.
Can you tie a blood knot with braid?
It is not recommended. Knot references describe the blood knot as a join for monofilament, and none of the sources checked support it for braid. For braid to mono, tie a double grinner knot, also called the double uni, with extra turns on the braid side.
How strong is a blood knot?
Figures of around 80% of the line's breaking strain are often quoted, but they are not independently tested. Tie one on the line you actually use and pull-test it before trusting it with a fish.
Why is it called a blood knot?
Nobody can say for certain. Knot reference sites say the name comes from the knots tied in a cat-o'-nine-tails, but treat that as folklore rather than recorded history.