Blood knot
Knot · Last reviewed 2026-08-10
The traditional join between two lines of similar diameter — neat, slim, and unforgiving of a large difference in thickness.
The blood knot joins two lines by wrapping each one's tag end around the other's standing part and passing both tags back through the gap in the middle, in opposite directions. When it is drawn up, the two sets of wraps pull against each other and lock.
It is the traditional knot for building a tapered fly leader, where several sections of decreasing diameter are joined in sequence, and it is used generally wherever two similar lines need a slim, tidy join that will run through rod rings without catching.
Its limitation is specific and important: it needs the two lines to be of broadly similar diameter. Join a heavy line to a much finer one with a blood knot and the fine line's wraps simply bite into the heavy one's without locking, and the knot slips. For a substantial diameter step, a different knot is required.
- Used for
- Joining two lines
- Holds in
- Monofilament, Fluorocarbon
- Do not use in
- Braid, Wire
How to tie it
These written steps are the instruction. The diagram supports them.
- Overlap the ends of the two lines by about 20 cm, running in opposite directions.
- Take the tag end of the first line and wrap it around the standing part of the second, five turns for typical diameters.
- Bring that tag end back and pass it through the gap between the two lines at the point where you started wrapping.
- Hold that in place and repeat with the second line's tag end, wrapping it the same number of turns around the first line's standing part in the opposite direction.
- Pass the second tag end back through the SAME central gap, but from the opposite side — the two tags must exit in opposite directions or the knot will not lock.
- Wet the whole knot thoroughly.
- Draw it up by pulling both standing lines apart steadily, watching the two barrels of wraps roll together and meet.
- Trim both tag ends close.
- 1. Overlap the ends of the two lines by about 15 cm.
- 2. Wrap one tag five turns around the other line and bring it back to the middle.
- 3. Wrap the second tag five turns the other way and bring it back to the same gap.
- 4. Pass the two tags through that middle gap in OPPOSITE directions, wet, and draw up.
Tying a blood knot
Knot · Verified — every stage checked against a canonical reference — reference: Knots Every Angler Should Know; How to Tie Fishing Knots — uni, blood, improved blood, surgeon's and loop knots · signed off by AI editorial review (Sprint 54) — every stage checked against the reference's numbered steps, rendered and inspected on 2026-08-18
Describe this diagram in words
Four panels. Panel one: two lines overlapping each other by a good margin. Panel two: the first tag taking five turns around the other line, drawn as a continuous strand passing alternately in front and behind, and returning towards the middle. Panel three: the second tag taking five turns in the opposite direction along the line, also returning to the middle. Panel four: the finished joint with a tight barrel of turns each side of a central gap, and the two tag ends leaving that gap in opposite directions — one upwards, one downwards.
How this drawing was produced
Redrawn in Sprint 54. The previous figure drew both sets of turns as disconnected diagonal dashes and printed LINE A and LINE B underneath paths that ran through them. The two tag paths are now generated by `weave()`, and the fourth panel shows the tags leaving the middle gap in opposite directions, which the old figure asserted in a label and did not draw.
Finishing it properly
- Match the diameters: a blood knot is reliable up to roughly a fifty per cent difference and unreliable beyond it.
- Use more turns in finer line — five for typical diameters, six or seven for very fine.
- Wet generously; there are two barrels of turns closing simultaneously and the friction is considerable.
How it fails
The blood knot fails when the two lines differ too much in diameter — the finer line's wraps cut into the heavier line's rather than gripping it, and the join pulls apart at a fraction of its expected strength. It also fails if both tag ends were passed through the central gap in the SAME direction, which produces a knot that looks right and unravels under load. Too few turns in fine line is the third cause.
A line-to-line knot for similar diameters, and the mistake of using it across a big step
The blood knot is chosen for one specific job — joining two lines of similar diameter neatly — and almost every problem with it comes from asking it to do a different one.
WHY IT IS CHOSEN. The finished knot is slim, straight and in line with both standing parts, which means it passes through rod rings smoothly and does not catch weed or hinge. That matters enormously in fly fishing, where a tapered leader is built from a series of these joins and every one of them must turn over cleanly, and in any situation where the connection must be wound onto a reel and back out through the guides.
IT NEEDS SIMILAR DIAMETERS AND THAT IS THE BINDING CONSTRAINT. The knot works by two barrels of wraps rolling together and locking against each other, and that requires both lines to bed down comparably. Join a fine tippet to a heavy butt section with a blood knot and the fine line simply cuts into or pulls through the coarse wraps — the barrels cannot lock because they are not the same size. As a rough working rule, a step of more than about one diameter grade is where it stops being the right choice, and the usual answers are more turns on the thinner line, or a different knot entirely.
BRAID AND WIRE ARE OUT. Braid is too slippery for the wraps to lock and wire will not form them at all. The record's `avoidIn` says so and there is no version of this that works.
WHAT TO USE INSTEAD, BY SITUATION. For a large diameter step — main line to a much heavier shock leader — a knot designed for the step is required rather than a blood knot with more turns. For braid to fluorocarbon, a slim double-uni or a purpose-designed braid-to-mono connection. For a connection that must be made quickly in the dark or in cold hands, a loop-to-loop, which is far easier to get right under those conditions.
AND THE FAILURE TO WATCH FOR is the tags exiting on the same side. The two tag ends must leave the central gap in opposite directions; if they both come out the same way the knot does not lock and it will draw up looking almost right. That is worth checking every time rather than trusting.
Practitioner consensus
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Established leader, tippet and connection practice in fly fishing.States this directlyCitation checked — the work exists and is described correctly
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Leader construction and connection practice in still-water fly fishing.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where to go next
Where it is used
- Dry fly fishingThe leader is a tapered series of monofilament sections and the blood knot is what joins one diameter to the next. Its own record excludes braid and wire, neither of which appears in a trout leader.
- NymphingThe same taper, plus the dropper: a blood knot left with one tag long is where a second fly hangs, which is how a team of nymphs is made without a separate device.
What these connections rest on (2)
Practitioner consensus — 2 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Dry fly fishing
Which knot a kind of fishing conventionally uses is established practitioner knowledge that converges across independent traditions and independent state agency guides, and it is labelled as consensus rather than as tested result. Nothing here ranks knots by strength: see `why-knot-strength-tables-disagree` for why that number does not exist.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly practice including leader construction, droppers and the joins between line, leader and tippet.States this directlyCitation checked — the work exists and is described correctly
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Long-running published description of British game angling practice, including leader and tippet construction.States this directlyCitation checked — the work exists and is described correctly
Nymphing
Which knot a kind of fishing conventionally uses is established practitioner knowledge that converges across independent traditions and independent state agency guides, and it is labelled as consensus rather than as tested result. Nothing here ranks knots by strength: see `why-knot-strength-tables-disagree` for why that number does not exist.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Stillwater fly practice including leader construction, droppers and the joins between line, leader and tippet.States this directlyCitation checked — the work exists and is described correctly
- Trout & Salmon — Bauer Media (Specialist angling publication)Relied on for: Long-running published description of British game angling practice, including leader and tippet construction.States this directlyCitation checked — the work exists and is described correctly
What it joins
- Fluorocarbon leadersJoining leader to mainline is a line-to-line connection, and blood-knot family knots are the conventional answer.
- Fly leaders and tippetJoining two lengths of similar-diameter monofilament is exactly what a tapered leader needs, and what the blood knot is for.
- Paternoster rigStanding line and dropper are two lengths of similar line joined mid-trace, which is exactly the blood knot's job.
What these connections rest on (3)
Practitioner consensus — 3 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Fluorocarbon leaders
The leader and the join that attaches it.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Knot selection for joining line to terminal tackle and line to line.States this directlyCitation checked — the work exists and is described correctly
- IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: The role of knots and connections in terminal tackle, and the line-class conventions that depend on them.States this directlyPassage read and verified
Fly leaders and tippet
The connection a fly angler makes most often, and the knot conventionally used for it.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Knot selection for joining line to terminal tackle and line to line.States this directlyCitation checked — the work exists and is described correctly
- IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: The role of knots and connections in terminal tackle, and the line-class conventions that depend on them.States this directlyPassage read and verified
Paternoster rig
The rig whose structure is a knot.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Knot selection for joining line to terminal tackle and line to line.States this directlyCitation checked — the work exists and is described correctly
- IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: The role of knots and connections in terminal tackle, and the line-class conventions that depend on them.States this directlyPassage read and verified
Worth understanding first
- Joining two lines: what the join has to surviveThe classic line-to-line join, and the record that explains why diameter mismatch is the constraint that decides whether it holds.
- Wetting, seating and tag ends: the three things that decide whether a knot holdsA blood knot tightened unevenly beds one side and leaves the other loose, and it fails at the loose side under the first heavy load.
- Why knots slip or breakJoining two materials of different stiffness is the hardest case, and it is where a leader join usually fails.
What these connections rest on (3)
Practitioner consensus — 2 connections
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Joining two lines: what the join has to survive
A mechanism edge from a record to the reasoning beneath it. How knots and rigs behave is established practitioner knowledge converging across independent angling traditions, and is labelled as consensus rather than as tested result.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive angling practice including knots, leaders, terminal tackle and the reasoning behind rig arrangements.States this directlyCitation checked — the work exists and is described correctly
- Still-Water Angling — MacGibbon & Kee, 1953 (Specialist angling publication)Relied on for: Stillwater angling practice including terminal tackle, hook holds and the mechanics of playing fish.States this directlyCitation checked — the work exists and is described correctly
Wetting, seating and tag ends: the three things that decide whether a knot holds
A mechanism edge from a record to the reasoning beneath it. How knots and rigs behave is established practitioner knowledge converging across independent angling traditions, and is labelled as consensus rather than as tested result.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive angling practice including knots, leaders, terminal tackle and the reasoning behind rig arrangements.States this directlyCitation checked — the work exists and is described correctly
- Still-Water Angling — MacGibbon & Kee, 1953 (Specialist angling publication)Relied on for: Stillwater angling practice including terminal tackle, hook holds and the mechanics of playing fish.States this directlyCitation checked — the work exists and is described correctly
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Why knots slip or break
A joining knot's characteristic failure is specific to joins.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Knot and leader practice, including material behaviour and seating.States this directlyCitation checked — the work exists and is described correctly
Instead of this
- Double surgeon's knotThe same job with the opposite trade-off. A blood knot is slimmer, more symmetrical and better through the rings, and it wants two lines of similar diameter. A surgeon's is quicker, tolerates any diameter step and any material pairing, and is bulkier. Where the diameters match and the join must travel through rings, the blood knot is the better answer; almost everywhere else the surgeon's is.
- Loop-to-loop connectionA blood knot gives a slimmer join that runs through rings; a loop-to-loop can be changed in five seconds with cold hands. Which matters depends on whether you are casting or swapping.
What these connections rest on (2)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Double surgeon's knot
Two state and national fishing-education sources group these knots as answers to the same question and separate them on the diameter constraint — the blood knot working best with lines of similar diameter, the surgeon's joining lines regardless of diameter or type.
- How to Tie Fishing Knots — uni, blood, improved blood, surgeon's and loop knots — Recreational Boating & Fishing Foundation (Take Me Fishing) (Angling or fisheries organisation)Relied on for: The double surgeon's knot sequence, and the grouping of knots by the connection each is for.States this directlyPassage read and verified
- Fishing Knots — which knot for which line — Vermont Fish & Wildlife Department (Government fisheries body)Relied on for: A state wildlife agency grouping knots by job and stating that the surgeon's knot joins lines regardless of diameter or line type.States this directlyPassage read and verified
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Loop-to-loop connection
The trade-off is described independently across traditions.
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: Leader construction using blood knots.Citation checked — the work exists and is described correctly
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Line-to-line joins in coarse practice.Citation checked — the work exists and is described correctly
Environment and conservation
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Discarded line and lost tackle
An environmental claim attached to the arrangement that causes it, held to the authoritative standard the predicate requires because tackle loss and lead use are matters of regulation and of published conservation evidence rather than of preference.
- Angling Trust guidance for anglers — Angling Trust (Angling or fisheries organisation)Relied on for: Guidance to anglers treating lost and discarded line and terminal tackle as an avoidable environmental harm and an avoidable cause of access loss.States this directlyCitation checked — the work exists and is described correctly
- Good Fish Guide — Marine Conservation Society (Conservation authority)Relied on for: That lost fishing gear persists in the marine environment and continues to entangle, which is the mechanism the discarded-tackle record describes.Background and mechanism onlyCitation checked — the work exists and is described correctly
History and culture
What these connections rest on (1)
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Nylon, and what synthetic line changed
Where a terminal arrangement came from and what it displaced, drawn from the angling literature and from widely restated practitioner accounts rather than from scholarship.
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive angling practice including terminal arrangements, leaders and knots, and the development of each within the sport.States this directlyCitation checked — the work exists and is described correctly
- Still-Water Angling — MacGibbon & Kee, 1953 (Specialist angling publication)Relied on for: Mid-twentieth-century angling practice written across the change to synthetic line, covering terminal arrangements and the materials they depend on.States this directlyCitation checked — the work exists and is described correctly
Sources for this page
- Knots Every Angler Should Know — Iowa Department of Natural Resources, 2015 (Government fisheries body)Relied on for: The sequence, the five-or-six turn count, and the requirement that the two tag ends leave the central gap in opposite directions.States this directlyPassage read and verified
- How to Tie Fishing Knots — uni, blood, improved blood, surgeon's and loop knots — Recreational Boating & Fishing Foundation (Take Me Fishing) (Angling or fisheries organisation)Relied on for: That the knot is two opposed clinch-style barrels, is for lines of similar weight, and finishes with both tags in the centre facing opposite ways. Used for topology only: this source's own step order is internally inconsistent and is recorded as such on the source.FishingHQ's interpretation of what it saysPassage read and verified
- Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: The construction of the blood knot and the requirement for similar diameters.States this directlyCitation checked — the work exists and is described correctly
- Still Water Fly-Fishing — Andre Deutsch, 1952 (Specialist angling publication)Relied on for: That blood knots are the conventional means of building a tapered leader from sections of decreasing diameter, in an independent game-angling tradition.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
How FishingHQ labels evidence is explained in the evidence policy.