FLY REEL · BACKING TO ARBOR
On most fly reels the arbor knot is a formality. It gets tied once, buried under a couple hundred yards of backing, and never thought about again — which is fine right up until something runs far enough that you can see the spool. The 100 Percent Arbor is for reels where that run is a real possibility. It starts with a doubled section of backing, so when the arbor finally gets pulled into the fight, two strands are wrapped around it instead of one thin one.
Six stages, and the double has to be solid before any of them count
Job
Backing to fly-reel arbor in high-load systems.
Prerequisite
A secure doubled backing section, commonly created with a Bimini Twist. Don’t skip checking that double on its own.
What it’s actually best for
Backing connections that might genuinely get tested by a long, hard run, not everyday light spooling. No knot compensates for a sharp or rough arbor edge, so I check the spool itself before I trust anything tied to it.
Why it exists
Its published design goal is to preserve far more of the backing’s rated strength at the arbor than a basic spool-start knot. That is why it exists. I still treat the percentage in the name as a reported test claim, not a guarantee: backing, knot quality, reel geometry and test method all matter.
Two strands at the arbor instead of one
The backing gets doubled first, then wrapped around the reel arbor and locked so two strands carry the transition rather than one thin backing leg. That’s a real difference from the basic Arbor Knot, which is there to get line started on a spool and isn’t asked to do much after that. It’s easy to call that difference theoretical, since almost nobody sees their arbor mid-fight. The trouble is you don’t get to pick which fish turns it into a practical one.
The double comes first, the arbor second
- Build a long doubled section in the backing first, commonly with a Bimini Twist, and pull-test that double before it goes near the reel.
- In the doubled backing ahead of the Bimini, form a large loop and tie a two-turn Nail Knot / Half Fisherman’s lock.
- Tie an overhand or double-overhand stopper in the doubled tag end and work it down close to the Nail/Half-Fisherman lock. Tighten the lock firmly before the spool enters the system.
- Fold the long doubled loop into a double loop and slip it over the removed fly-reel spool.
- Pull the standing backing to slide the locking knot tight against the arbor while working the main line back and forth until both spool loops close completely.
- Load-test the finished arbor connection before winding backing over it, then reinstall the spool and finish spooling.
Failure clue
The doubled section underneath it was weak to start with, which usually means the Bimini feeding it wasn’t checked on its own before it got put to work here. The legs crossed on the arbor. The knot settled onto a rough edge, which is a reel problem more than a knot problem. Or the attachment never got load-tested and then a few hundred yards of backing went over the top of it. That last one is the only one you can still do something about, and the window closes the moment you start spooling. I check mine every single time now, because I only get away with skipping it until the one time I don’t.
Only worth it if a fish can reach your backing
Use: fly/offshore systems where reaching the arbor is plausible and backing connection matters. Skip: ordinary light spooling where a simple Arbor Knot is sufficient. Compare: Arbor Knot simpler; Bimini Twist supplies the doubled section.
How I check this one before it ever sees line over it
I pull-test the doubled arbor knot against the reel by hand, harder than I expect any fight to actually load it, before a single wrap of line goes over top. Once it’s buried under backing I can’t inspect it again without stripping everything off, so this is the only window I get. NetKnots’ 100 Percent Arbor page is worth a look for the tying sequence itself, but the habit that actually matters is the pull test before you spool, not the knot alone.
FIELD DECISION
A knot called 100 Percent still has to fit your spool
Best for: high-load fly-reel backing to arbor.
Field tieability: Medium. Tie it before you spool. It isn’t a repair you’ll be making on the water.
Requires first: Bimini Twist
Compare next: Arbor Knot · Bimini Twist
Open the deeper knot workflowJob, material, route, dressing, seating, pull-test checks and the standardized comparison record.
THE SIX-MOVE CHECK
Job → Material → Route → Dress → Seat → Test
- Job. Name what the connection has to do before choosing the knot.
- Material. Confirm the line, leader, rope, wire, and hardware actually suit this structure.
- Route. Trace every pass before tightening anything.
- Dress. Put strands, wraps, and loops in their intended order with no accidental crossings.
- Seat. Tighten in the order this knot needs. More force does not repair bad geometry.
- Test. Inspect the finished shape, load it by hand when appropriate, and retie if anything moves or fails the article-specific checks.
Practice / pass test. Tie this knot three clean times without rushing. A tie passes only when it matches this article’s What to check before you trust it geometry, shows none of the listed failure clues, and survives the stated load/inspection test. If you cannot tell why one attempt is better than another, keep practicing—the lesson is recognition, not memorization.
KNOT SPEC
100 Percent Arbor Knot — the short answers
- ALSO CALLED
- Also written as the Hundred Percent Arbor Knot. The name is a claim about retained strength, not a measurement you should quote. Used mainly by fly and offshore anglers who expect a fish to reach the backing.
- KNOT TYPE
- Arbor knot tied in doubled line, locked around the spool
- WHAT IT CONNECTS
- Backing to fly-reel arbor in systems where a fish can plausibly run to the spool. Not a terminal knot and not a general-purpose spool knot for casual line fills.
- LINE TYPES
- Fly backing — braided Dacron and gel-spun. Gel-spun is thin and slick enough to bite into a spool or into itself, so watch how it seats. It is not a mono knot in normal use, and not a terminal-tackle knot at all.
- STRENGTH BAND
- Designed as a high-strength arbor connection. The published source names it for a reported 100% backing-strength result, but that number should not be treated as universal across backing, reel geometry, tying quality or test rigs. The useful claim is narrower: this is a purpose-built loaded backing connection, and it is only as sound as the doubled section and locking system feeding it.
- DIFFICULTY
- Advanced, mostly because of its prerequisite. The arbor moves themselves are moderate; the doubled section — usually a Bimini Twist — is the part that takes practice. Not a beginner or a children’s knot.
- STEPS AND WRAPS
- Six moves after the double is built: form a large loop in the doubled backing, tie a two-turn Nail/Half-Fisherman lock, add an overhand or double-overhand stopper close to that lock, fold the doubled loop over the removed spool, slide the lock to the arbor, then work both loops completely closed and test. The prerequisite doubled section is a separate build.
- TIE TIME
- Slow — a home knot, emphatically. Several minutes including the Bimini. It is not a repair you make on the water, and it should be tied at the bench before spooling.
- POOR CONDITIONS
- Poor. This is a bench job with good light and both hands free. If you are trying to tie it on a rolling deck with cold hands, you are tying it at the wrong time.
- THROUGH THE GUIDES
- It never passes rod guides. The equivalent question is whether the finished knot lies flat on the arbor and cannot rotate onto a sharp spool edge or into a line-guide slot.
- LUBRICATION
- Wet the doubled section before you seat the locking turns. Two strands drawing down together generate real friction, and Dacron backing in particular scuffs when pulled down dry. The prerequisite Bimini also wants lubrication.
- TAG END
- Trim the tags close but not flush, and keep them short enough that they do not lump under the first layers of backing. Long tags under hundreds of yards of fill create a ridge the backing digs into.
- TOOLS
- None strictly required, but a knee or a second pair of hands helps with the Bimini. Clippers to trim. Good light matters, because this is the last look you get at the connection.
- BEST SUITED TO
- Fly and offshore fisheries where reaching backing is plausible — tarpon, bonefish, permit, salmon, steelhead, tuna on the fly. Not worth the effort on a light trout reel that will never see the arbor.
The strength bands are rough on purpose. Published knot tests don’t agree with each other — the same braid-to-leader knot has tested near ninety percent of line strength on one machine and under half on another, because the line brand, its diameter, how fast it got cinched, whether it was wet and whose hands tied it all move the number more than the knot does. Use the band to compare this knot with the others, not as a number to quote.
FIELD INTELLIGENCE
Where it earns its place, and where it costs you
Advantages
- Two strands take the load at the arbor instead of one thin backing leg, which is a real structural difference rather than a marginal one.
- It keeps genuine strength at the one connection in the system that is normally treated as a formality.
- It seats flat around the spool, so it does not create a hard lump under the fill.
- It removes a known weak link from any system where a fish can plausibly run to the backing.
Disadvantages
- It depends entirely on a doubled section you have to build first, and a poor Bimini makes the whole thing pointless.
- It is slow and fiddly, and it cannot be tied on the water.
- It is overkill on ordinary reels where the arbor will never be seen.
- Once buried under backing you cannot inspect it again without stripping the reel, so the pre-spool check is your only window.
- It does nothing about a rough or sharp arbor edge, which is a reel problem no knot solves.
Use a different knot when
- Arbor Knot — when the reel will never run down to the spool — ordinary light spooling does not need this
- Bimini Twist — not an alternative but a prerequisite — it is what supplies the doubled section this knot is built on
- The reel’s own backing attachment — when the manufacturer provides a designed anchor point, which outranks a generic knot
- Uni Knot to the arbor — when you want a simple, quick and adequate spool connection and are honest that adequate is enough
WHAT TO CHECK BEFORE YOU TRUST IT
This knot earns its place on one day in several seasons, and that is exactly the argument for it. Most reel-arbor connections are never tested, so most anglers never learn theirs was weak. Treat the arbor as part of the fighting system: they check the doubled section on its own before it goes near the reel, they make sure the two legs stay parallel and never cross on the arbor, and they pull-test the finished connection hard by hand before a single wrap of backing goes over it. The tradeoff is time and prerequisite skill, spent against a risk that rarely arrives.
What actually makes it fail
- A weak doubled section underneath it — usually a Bimini that was never checked on its own before it was put to work.
- The two backing legs crossing on the arbor instead of lying parallel, so one leg takes the load and cuts into the other.
- The knot settling onto a sharp or rough spool feature, which is a reel problem the knot cannot fix.
- Skipping the load test and then burying the connection under hundreds of yards of backing, where you cannot reach it.
- Seating the locking turns dry, which scuffs Dacron backing where the strands slide against each other.
How to test it, and how it ages
Test the doubled section by itself first; if the Bimini is poor, nothing downstream matters. Then seat the arbor connection by pulling both doubled legs evenly and look for three things: backing lying flat around the arbor, the two legs still parallel, and the knot unable to rotate into a sharp spool feature. Finally, pull-test against the reel by hand — harder than you expect any fight to load it — while controlling the spool safely. Do all of this before a single wrap of backing goes on, because the window closes when you start filling.
Over a session: It lasts the life of the backing, buried and untouched, and it does not loosen the way a wrapped terminal knot does. The thing that ages is the backing itself; when you strip and replace backing, retie the arbor connection rather than reusing it.
Troubleshooting
Is this actually worth tying instead of a plain arbor knot?
Only if a fish can reach your backing. On a fly or offshore reel where that is plausible, yes. On a light trout reel, the plain arbor knot is honestly enough.
Why does the connection feel weak even though I tied it carefully?
Almost always the doubled section, not the arbor knot. Check the Bimini on its own before it goes near the reel.
Why do my two backing legs keep crossing?
You are building the locking turns too fast. Lay them on with the legs held parallel, and if they cross, back out rather than tightening over the top.
Can I tie this on the water if my backing breaks?
No, and do not plan to. Build it at the bench before spooling. A field arbor repair is a plain arbor knot and a short day.
How do I inspect it once the reel is full?
You cannot without stripping the backing. That is why the pull test before spooling is the whole discipline of this knot.
