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MBS (Minimum Breaking Strength) on Climbing Gear is a Myth
🕑 Added 2021-08-11 13:43:50 +0000 UTCMBS or minimum breaking strength is great for comparing one product to another and I appreciate having standards on life supporting gear, BUT to boil down a piece of gear to only 1 single number doesn’t tell the whole story and we discuss gear, their ratings and value and limits of backyard science.
MBS is Minimum Breaking Strength and usually printed or stamped onto most gear and is 3 break tests calculated with a 3-sigma rating means that 99.9% of the products are stronger than the reported MBS rating. If you calculated the average, then 50% of everything would break below that MBS number. 3 sigma ratings more accurately represents a product’s strength….. AS LONG AS YOU USE IT LIKE THEY TESTED IT
That is how MBS is calculated, but how is the gear tested. Short answer is idk: most of us don’t know. I do know ropes are usually done with larger diverters to preserve the strength since knots give such a variety of results. I do know that carabiners are usually pulled at a specific speed with a 10mm pin. But a lot of the standards are either boring af and/or behind a paywall. I appreciate standards and the committees that make them. Standards help us compare one product to another as fairly as possible. However, my backyard science isn’t doing standards but how I have personally used the gear or have seen it used, whether or not it was according to the recommended use. I like my kind of science.
So last year, I made a video about CMI hangers where I tested them in shear by bolting them down to concrete and got 34kn in all three of our tests or around 7,700lbf and not 10,000. My delivery of that video was unprofessional so i took it down.
But now I’m even more curious why they broke below 10,000lbs since they told me they did a lot of tests, that it meets standards and a 3rd party also messaged me and said they also did a lot of tests and it always broke above 10,000lbs. Now, no one was telling me the CONTEXT of HOW it was tested which I feel would be helpful since I’m guessing over here. No I’m not paying for and reading the UIAA and CE standards. I try to test gear in the way you and I use it so we understand it better, I’m not trying to replicate an already rigorous and thorough process. I attached it to the ground like I thought it was intended to be used, since I have seen numerous real world applications of it being attached to rock and being pulled in shear. However, the CMI company has specialized towards the arborist industry and these hangers are intended to be put in trees and pulled straight out, or tension or axial, rather than shear.
CMI HANGERS IN TREE We tested these in a tree since that is how they are intended to be used. ***In shear we got 30.48 before bolt sheared off but hanger started to tear, ***42.74 tension when my puller got damaged and again at 42kn before bolt pulled out ***Another one in tension pulled out at 42.48 and started to tear the hanger. ***So a few conclusions: 1 - it doesn’t matter if a ⅝” bolt comes out first and 2 - pulling in shear is putting all the force on one side. Tension pulls on both sides more evenly.
CMI HANGER IN SLACKSNAP In our SlackSnap or slow pull machine, we got 37.30kN with a quicklink and 48.44kN with a large shackle. We found the larger shackle got us 10,000lbf which is the clue to how they achieve 10,000lbf.
The CMI’s website is found at https://cmigearusa.com/products/bhanger?variant=640162233
OUR CUSTOM 6mm THICK 316L STAINLESS HANGER - (Thank you Rune from Norway) ***Using a ⅜” Titan HD concrete screw in granite, the bolt sheared off at 46kN both times ***In Slacksnap machine, we got 65.20KN ***Conclusion: The smaller shape AND the different type of steel helped get an 20kn.
MONSTER CRUXES broke at the weld lower than 60kn
WAVE BOLTS broke around what they state, but they break lower also
FIXE HELY most broke above 28kn but some at 27kn KNOTS break at 50% of MBS
CONCLUSION No single breaking strength number can give you everything you could know about your gear, but it kinda gives you all you “need” to know. Super good enough. So be nice to gear companies so they don’t hate me, realize only knowing MBS is a limited understanding of your gear, and subscribe so you can see future videos of us testing things with backyard science. I’m amazed you read all of that!
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00:00 MBS is a Myth 05:45 Load cells are accurate 06:44 Testing CMI hangers in a tree 11:51 Testing CMI hangers in SlackSnap 15:40 Testing custom SS 6mm hangers 18:11 Conclusions 19:07 Other things break below MBS
