Knot Strength – Updated with Fly Rod & Reel Video

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    Zach Matthews
    The Itinerant Angler

    Guys –

    I am working on an article for Fly Rod & Reel magazine which is going to be very, very cool.  A friend showed me how to make welded loops at home, and we’re going to demonstrate the technique in the article and with video.  The article is neat for other reasons but for purposes of what I did last night, that’s all you need to know.

    So I performed some break-strength tests.  I took ordinary 20 lb. bulk monofilament from Wal-Mart (Shakespeare), and I did the following tests using Rio 5 weight fly line and my Boga Grip, with the line end looped around a clamp on my desktop:

    Knot Break Strength (Test 1 | Test 2)

    • Nail Knot (5 Turns) 10 lbs. | 10 lbs.
    • Albright Knot (5 Turns) 12 lbs. | 12 lbs.
    • Doubled-Line Nail Knot (6 Turns)   8 lbs. | 10 lbs.
    • Double Surgeon’s Knot (20 lb. to 20 lb.) 14 lbs. | 18 lbs.
    • Castwell Knot 13 lbs. | 12 lbs.
    • Welded Loop 20 lbs. X 3 attempts

    I was shocked.  Flat out shocked, by lots of these results.  Firstly, I have been using 20 lb. mono nail-knotted to the end of my fly line for years.  I have never, ever broken a trout or any near-shore saltwater fish off at the nail knot.  That just goes to show how much pull 10 lbs. actually is; in fact, that’s about where tarpon anglers set their drags.

    I was also surprised that the Doubled-Line Nail Knot, where the line is doubled over inside the knot in order to make a “bump” at the end so it can’t slip off, was actually weaker than a standard nail knot.

    I was not surprised that the Albright Knot is the strongest tied knot of them all; that is the one I switched to for striped bass after I had an actual nail knot fail (stripers ain’t trout).  I was a little surprised that it was only a 20% improvement on the nail knot, however.

    I did the Double Surgeon’s Knot test just to confirm I didn’t have like weak material or something.  The first, 14 lbs., result, I think was an anomaly.  I must not have wetted the knot properly.  The second, 18 lbs., result, is about what I would expect – the Double Surgeon’s is supposed to be 90% of the break strength of the material, and it was.

    So that leaves the biggest shocker of all: the welded loop.  I have made several welded loops and tested them; even the most lackadaisical efforts make knots which test out in the mid-teens, and on the one I took the most care with, as documented in a video to be released with the article, it was TWICE as strong as any other knot, and it survived being pulled to that break strength three times before it failed.  From what I am told, the factory welded loops are even stronger than that (I didn’t care to sacrifice one in testing).

    Bottom line is, welded loops are strong!  Whether you make them at home or buy them on the line; I think the key must be the stretchability.  The knot can’t fail until the weld reaches its break point, and it won’t do that until almost the core break strength of the line itself (5 weight line is actually only rated to 20 lb. test anyway, and in one of my earlier tests, the core broke but the weld didn’t).



    Guys –

    The article I did these tests for is out in Fly Rod & Reel magazine, on newsstands now, so here’s a link to the video I promised:


    Mike McKeownMike McKeown

    Things that make you go hmmmmm….

    Kent EdmondsKent Edmonds

    Thanks Zach. Interesting, if a little frightening (though I too have gone to Albrights or home-made, double locked braided loops on striper rigs).

    – Did std. nail knots break in knot, in line outside knot, or just slide off?
    – Did albright break in knot or line?
    -I’m guessing (since you were using the boga) that testing was with steady pull? Would you expect different results with jerking stress?

    It might be interesting to try with a premium mono and see if are comparable.

    Kent - FlyFishGA

    Zach Matthews
    The Itinerant Angler

    Kent –

    It was a steady pull; I put a clamp on the edge of my desk and used that to hold the line (wrapped it around one of the legs of the clamp), then I attached the Boga to whatever system it happened to be using a Double Surgeon’s Loop.  Then I slid the Boga backwards along the desktop until the system broke.  So no jerking.

    The nail knots all failed by stripping the coating off the core and sliding off, including the double nail knots.  As I recall, the Albrights failed the same way but also unraveled; the coating was partially slipped.  When the weld eventually failed, it peeled up from the rear, which as I understand it is how they usually fail in the factory too.

    I think premium-grade material would get you higher overall numbers before failure, but I would expect the ratio of which knots failed first and how to remain the same.  It looks like the Albright is 20% stronger than the nail knot,  for example, and I would expect that to remain true regardless of material.

    The actual 20 lb. monofilament never broke in any test, including the Double Surgeon’s knot test; it always either slipped the line or the knot eventually unraveled.

    Zach Matthews
    The Itinerant Angler

    Hey guys –

    Some people have been communicating with me about making those welded loops; here’s one method that looks very easy.

    That is different than the way I have been doing it so I can’t speak to the strength but I bet it would be quite strong.

    Phil BrnaPhil Brna

    Zach, you should try testing braided loops using 50# gubrod braided mono as well.

    Kent EdmondsKent Edmonds

    Phil, not much doubt that the 5 wt flyline would break before the 50# Guidbrod loop.

    Kent - FlyFishGA

    Phil BrnaPhil Brna

    Oops! I was looking at the knot strength part and not the 5 wt part.


    Do you take requests, Zach?

    I’ve always wanted to do a knot strength test on the weaver’s bend knot, aka the “castwell knot” linked here:

    It’s about the simplest line to leader connection conceivable and seems to have pretty good strength.


    Dang Zach I’ve been preaching about not tying nail knots on fly line for a long time. The Castwell knot works much better if you don’t have braided loops.

    There are two ways to tie an albright. The easiest one you wrap lighter line from the bottom and twist up then back through the loop on the heaiver line. The other one (proper) starts at the top and twists down. The easy one is very strong but not as strong as the proper tie.
    For line to line of similar size I prefer a blood knot.

    BD next time we fish I’ll show you a better loop then the perfection. I’ve not done any official tests on it but my time on the water proved to me that it’s a relatively weak knot.


    Man, I learn something new every day. Somehow I have managed to fish for a long time without ever seeing the “castwell knot”. That looks too good to be true. Does it actually work? It seems WAY too easy. I will be trying that out for sure.


    OK, I just tried this knot. It is incredibly simple and appears quite strong. I may be a convert. Good info….

    Zach Matthews
    The Itinerant Angler

    The Castwell went to 13 lbs. | 12 lbs.,


    Andrew I used it for a long time using 20 pound straight leaders. The loop knot fails 95% of the time. I could count the times the castwell failed on my hands. My test method was getting flies hung up in deep water and pulling till something breaks the 20.

    I use braided loops now because I prefer not cutting my fly line every time I retie a new leader. It’s still a great knot to know for when you need a quick line to leader connection.

    R Black

    When will the info be available ?


    Agreed Mike. Not the perfect knot for every situation, but a very useful knot for many scenarios. Thanks to you and BD for the info.

    Zach Matthews
    The Itinerant Angler

    I’ve been testing different qualities and methods of making the welds now, including the way the Spey Pages guys do it.

    Chris BeechChris Beech

    Where is this article going to be published, Zach?

    Best Regards,


    Justin WittJustin Witt

    I feel a little silly jumping in here with all this awesome science going on, but it seems like since what I’ve been doing to create “welded” lops on flylines has worked well for me all these years and it doesn’t seem to have gotten mention yet in the thread, I should probably at least see if it floats.

    Zach Matthews
    The Itinerant Angler

    Guys the article is out in the next issue of Fly Rod & Reel, which some people are already receiving in their mailboxes.


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