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Spanset Break Tests


There are a number of ways that slackliners use slings, which are typically spansets, that are non-standard. Until now, we just believed that because of how strong spansets are, that no matter how we rigged with them we could be sure that they would be strong enough. Well, I wanted to test a few different methods that are commonly used by slackliners to see just how strong the spansets actually are.



For all of these tests, a slow-pull destructive test was done using a hydraulic pull testing machine. Each test produced a graph with time on the X-axis and force on the Y-Axis. All tests were done using Green Spansets of various lengths, depending on the test.




The Sliding-X with 4 connection points
4-point Sliding-X 4-point Sliding-X

We used four connection points with the sliding-x. Each point was connected to the green spanset with a 1/2" Shackle. We initially used steel carabiners, but the carabiners broke before the spanset did (comforting). So we had to redo the tests with a stronger connector. The master point went to a large, 1" shackle that was connected directly to the hydraulic cylinder.

The force we achieved was 66,550 lbf (296 kN). Given that our spansets have a 5:1 safety ratio, the green spansets have a 13,310 lbf working load limit with this configuration.


Girth Hitching Two Slings Together
Girth Hitch Girth Hitch

We connected two green spansets together with a girth hitch and then pulled them to destruction.

The force we achieved was 21,420 lbf (95.3 kN). Given that our spansets have a 5:1 safety ratio, the green spansets have a 4,280 lbf working load limit with this configuration.


Sling Shortener Technique
Sling Shortner Sling Shortner

We used the Adjustable Length Spansets technique and pulled the sling to destruction.

The force we achieved was 18,030 lbf (80.2 kN). Given that our spansets have a 5:1 safety ratio, the green spansets have a 3,600 lbf working load limit with this configuration.



The results were quite surprising for the adjustable length spansets technique as well as the girth hitch technique. I thought for sure that the girth hitch would have a lower force than this and vice versa for adjustable length spansets.

Given the max forces we use in slacklining, these numbers are very comforting. Using any of these techniques with any type of slackline, we can be confident we will be well within the working load limit of our slings.

Given the past testing done with spansets by the manufacturer, these results can be extrapolated to all the spanset types. This means that we can apply these results to the purple spansets as well. Here is a nice chart with the breaking strengths and working load limits for both green and purple spansets:


Method Purple Spanset Green Spanset
4-Point Sliding-X 29.6 kN (6,650 lbf) 147.9 kN (33,250 lbf) 59.2 kN (13,300 lbf) 296.0 kN (66,550 lbf)
Girth Hitch 9.5 kN (2,125 lbf) 47.3 kN (10,625 lbf) 19.0 kN (4,250 lbf) 95.3 kN (21,420 lbf)
Adjustable Length Spanset 8.0 kN (1,800 lbf) 40.1 kN (9,015 lbf) 16.0 kN (3,600 lbf) 80.2 kN (18,030 lbf)

Future Research

I'd like to test a few other methods of use with the spansets in the future, maybe 3-point sliding-x and the overhand knot. If you have any other methods that you would like to see broken, please mention them in the comments below. Once again, thanks for reading, I hope this info is helpful to you folks out there!

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17 thoughts on “Spanset Break Tests”

  • What's about spanset with tight knot on it which is then jammed inside a crack? I can send a picture for better explanation :)

    • That would be interesting to test. However, i'm unsure how I could arrange that in a pull testing machine without lots of custom work. Once I build my own, I should be able to do something like that.

      • Would be great. Thanks for that thread - it's really useful - I was just wondering with Jordan about all of this configurations, thinking 'it would be great if someone could test it' :D

  • you could test to see if its safer to thread your rigging plate on the spanset then connect the ends with a shackle then test regular basket config.

    • The rigging plate is far weaker than the spanset and it will likely break WAY before the spanset will. This method done no harm to the spanset what-so-ever and it applies the same loads as a normal basket configuration with the same angles.

  • More fantastic research!

    I long line more than I highline and thus use trees for ancores. So

    1. From the existing data can you extrapolate the breaking strength of a span set in a basket (girth hitched) around a tree. For a green round sling would it be 4240(1WILL)*5(MBS)=2120(max breaking strength)?
    2. For a basket in green would it be 10600*5=53000lbs or/250 212kn?

    • Answers to your questions:

      1.) The strength of a green spanset girth hitched around a tree is 5 times the working load limit of the choker hitch (same as girth hitch), which is 4,240 lbf x 5 = 21,200 lbf.

      2.) The basket strength of a green spanset is indeed 5 times the working load, which would be 10,600 lbf x 5 = 53,000 lbf. Remember that 1 kN = 224.8 lbf, so the kN rating is 53,000/224.8 = 235.77 kN.

      Also, keep in mind, these MBS numbers correspond to a brand new sling. The reason for such a large safety margin between the working load limit and the breaking strength is because the more you use the sling, the weaker it becomes (typical of all woven substrates). Thus, you should mainly focus on the working load limit and never surpass it.

  • Hey Jerry, are you giving a 5:1 WLL reported for the spansets? The ones that I see around here in Europe and in New Zealand have a 7:1 safety factor. Which actually fits with your results. The 4 point sliding-x configuration can be seen as the same as a basket configuration. The 2 tonne WLL of a green spanset would then be 4 tonnes with the UBS of 14 tonne going up to 28 tonne which is more or less what you see with the configuration (296 kN).
    The girth hitch is pretty similar to a choke configuration with a reduction of strength by about 20% (to 1.6 tonnes) from the straight pull WLL of 2 tonnes. Theoretically it should give 14 * 0.8 = 11.2 tonnes UBS. Interesting to see that it is a bit lower at about 9.5.
    I was surprised by the strength reduction in the adjustable length spansets.
    How many tests did you run? Can you give some kind of indication of standard deviation or were they just single tests?

    • As mentioned above, the safety rating differs from one manufacturer to the other. In the US, spanset safety ratings are either 5 or 6-to-1, which is why the working load limit is slightly higher (2 metric tonnes for green (4,400 lbf) in Europe compared to 5,300 lbf in the US). Their ultimate breaking strength is quite similar (30,800 lbf for EU spansets and 26,500 - 31,800 lbf for US spansets).

      Interesting observation that the 4-point sliding-x is similar to a basket. I didn't think about it that way. I guess the way it's configured, it's very similar to a basket. Similarly for the girth hitch and choker hitch. However, I figured the girth hitch would differ slightly simply because there is more material in contact with eachother, which can negatively effect the strength.

      I only ran one test for each configuration, but because the manufacturer has done 1,000's of tests with these slings and their standard deviation is so low, we were both confident that these numbers were accurate representations of the actual breaking strengths. Not to mention, the safety ratio will take care of any minute fluctuations.

  • Michael Archer - January 29, 2014 at 11:25 am

    Hey Jerry Mike here from Stasis Inc. we commonly use figure 8 knots to shorten the span set to locate our fix point closer to the anchor any possible way to add a figure 8 break test next time. As well as possibly doing a shock load of a 3 foot spanset. I have Been seeing lots of people using 3 footers to back up their soft point or their. Pulleys. Just wondering your thoughts on that

    • Hey Mike,

      I have already considered doing the overhand knot, but a figure-8 knot would be good as well.

      As far as the shockload test, I do not have the capability to do this at this time. However, because of the elastic properties of most slackline webbing, I doubt the shockloads would be too extreme if the pulley system were to break and the spanset were to be loaded. I'm confident the force wouldn't even come close to the working load limit of the green spansets.

  • Hey Jerrry all of this is awesome work, and for us slackers its great to know about so thanks for the hard work. As far as other possible tests? How about a 3 point sliding x? I know that I've seen many highlines with only 3 bolts. I would be curious to see how it is compared to the 4 point. And even a 2 point sliding x would be really cool to see. I also use figure eights to shorten spansets and I've even put a figure eight into one side of a basket configuration around a tree to get the perfect distance. I wonder if that would significantly change the WLL of the basket? Any of these would be cool to see tests done for. Thanks again Jerry!

  • any possibility of a video of the spansets breaking in the future?

  • Also another good one would be to test each part of a spanset for its strength for example 550 paracord the outer sheath is rated for 250pounds and each inner strand is like 30 some odd pounds

    • The sheath of a spanset does not contribute to the strength at all. The core yarns hold about 97% of the load, which makes them the vital part of the sling. The double-wall tubular is only to protect the load-bearing core yarns.

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