I was climbing at WCJ today and fell off just above 2nd bolt on Final Apocalypse (7a+). I proceeded to smack my belayer and nearly the ground as the nut flew off and the hanger came off the bolt.
I was wondering if anyone had any info/suggestions as to why this happened? The bolts all looked in very good condition (new even). The hanger was loose although my partner tightened the nut with his fingers just before I fell. The bolt didn’t shear at all, the hanger looked completely undamaged. It’s also worth mentioning the nut didn’t break straight away, I had what seemed like quarter of a second of hanging before it broke.
I realise just how lucky I was to not deck, but I also think it was just a freak accident-any suggestions as to why it happened would be great!
Good to hear you're not hurt.
If I understand you correctly, the nut securing the hanger either broke or came off the thread of the bolt. You say the thread of the bolt was undamaged.
Did you find the nut? If so, was it damaged in any way?
Did your partner say anything about the nut when they screwed it back in place? How well it fitted, for example.
Finger tightened nuts are pissing into the wind, normal practice in an engineering environment is to use loctite to prevent loosening after torque tightening, not sure if that is defined as good practice for climbing purposes off the top of my head.
Yes, we believe either the nut itself sheared or snapped in some way. Yes, the thread on the actual bolt was completely undamaged, and I know how bloody difficult it is to shear threads (even if nuts are made of softer materials) but I also know how hard it is to snap a nut!
We tried to, but when I said it flew off I really mean it! It also landed in a lot of undergrowth which didn’t help.
So when they initially found it, the hanger could rotate 360* so they finger tightened it to stop that. Apart from that, they said it looked perfectly fine.
But the strength of a nut and bolt isn’t due to how tightly it is tightened, but the forces between the opposing threads. As long as the whole nut is engaged with the bolt’s thread (as it was) I don’t see why this would make a nut and bolt any weaker?
RE tightening, I know of some people who bring small spanners with them-might be something I should invest in!
Before the technical bog down gets fully underway. Was it the right nut?
The “thread”” on belaying at a indoor wall had a link to deaths in Yosemite one was the nut detaching
Yes, I always have a 17mm/19mm spanner on my sport rack. I use it often.
Could it have been a 1/2 nut (AF 3/4) on a 12mm bolt, or a 10mm nut (i.e 17) on a 3/8 bolt or some sort of mix up like that?
The vast majority of a tensile load capacity in a bolted joint comes from the tension in the bolt created by the nut being torqued to the correct capacity. Explanation here:
I can happily give other references if necessary but that is a reasonable source of info.
The BMC guidance on good bolt installation is here:
Not much time is given to tightening in the document but it is there and it is important.
Tightening to correct torque is important, but I'm surprised to hear of a nut coming off the bolt in a fall (the load can only approach 2* maximal impact force of rope very very worst case for a leader fall, for fun let's say that's 17kN), unless the nut was only on partially screwed on, surely something else is happening there?
The theory of bolted joints has no relevance to bolts used in climbing, when they approach even 50% of their failure strength there is no relevant contact between the hanger and the rock. With the common wedge bolts used in climbing the torque is only to check the bolt engages enough in the rock to achieve the rated pull-out resistance, whether they are correctly torqued, torqued and then loosened or never initially tightened makes no difference to their strength or pull-out resistance.
Sounds like the nut has untightened itself to the extent that it has come off the bolt.
If it was already effectively loose as you describe, then maybe vibration or the rope running against the right hand side of it was enough to totally detach it from the bolt?
May have been the case, but talking to my friend who tightened it by hand said the but seemed to fit absolutely fine and that it tightened perfectly...
Well is was tightened just before I fell on it, and before then the route was tried effectively on top rope so I think that is unlikely that vibrations caused it to loosen.
I also want to make it clear, it wasn't just a small nudge off the edge or something, it seemed like the nut really exploded!
Unfortunately without the nut we will never know if it was nut/thread failure or if it popped off the end having unwound so there is little point speculating especially as the remaining stud appears to be undamaged.
For reference the bolt and nut are compatible and are 5 years old, good quality M12 stainless steel with Bolt Products rod hangers.
Bolts do come loose from time to time for various reasons even if they were cranked up perfectly so having a spanner is a helpful tool to carry for crag maintenance.
I'll ensure someone from the local bolt fund takes a look at this sometime soon.
Hope you and your belayer are ok?
> Well is was tightened just before I fell on it, and before then the route was tried effectively on top rope so I think that is unlikely that vibrations caused it to loosen.
Only hand tight though. Would you drive a car where the wheel nuts have only been fastened by hand?
> I also want to make it clear, it wasn't just a small nudge off the edge or something, it seemed like the nut really exploded!
No damage to the bolt - stripped threads, etc. either means that the nut disintegrated, or that it simply became unthreaded. Logic and experience dictates that nuts don't just fail in such a catastrophic manner through normal loading.
As for the feeling that the 'nut really exploded', that would be exactly what it would feel like if you fell on it at the same point it became detached from the bolt.
I know it doesn't affect the bolt's holding force in the rock, however a properly tightened nut will mean that the hanger is loaded correctly (assuming properly positioned in the first place) and that the load is transferred to the bolt on an optimum fashion (i.e. Not in bending).
It just seems silly not to do the last bit properly when there is so much effort put into appropriate bolt selection and installation.
Thank you for clarifying.
Might it be worth recruiting a metal detectorist to look for the nut or nut fragments?
To me this sounds like the wrong nut. The wrong nut can feel fine on a slightly smaller thread. Finding it would be good because if this is the case there may be more of them around there.
Any chance that the person tightening was actually loosening the nut and then the nut tightened itself in the last bit of thread on grime or small amount of corrosion in the thread? It's an easy mistake to make, especially if there isn't much in the way of protruding from thread to judge whether you're tightening or loosening!
No disrespect intended, it's just a potentially a possibility.
The only way this could be the wrong nut is if the original came off after installation. These come out of the box from the manufacturer as a complete unit of bolt, washer and nut. They are not pieced together with scraps off the workshop floor or recycled from another route.
In an idea world a resin bolt properly installed is going to be the best solution but there are occasions that a quick to install expansion bolt is logistically preferable.
A correctly tightened up bolt hanger on perfectly smooth rock is unlikely to budge but when the rock isn't completely smooth the natural flex that occurs when the hanger is loaded will crunch the protrusions under the hanger and thus contribute to it working loose. It is not totally dissimilar to a toothed T nut slowly drawing into the plywood (new wall spinner syndrome.)
One possible solution is to add a nylon locking nut or glue but this has its own drawbacks as the nut may bind too tightly and rotate the entire bolt in its hole so it can't easily be removed or tightened.
Indeed. However, you can never know what may have happened to a bolt that has been up for a while really, however unlikely tampering may have been.
> One possible solution is to add a nylon locking nut or glue but this has its own drawbacks as the nut may bind too tightly and rotate the entire bolt in its hole so it can't easily be removed or tightened.
Do you know if anyone has ever researched using a second nut as a jam-nut to secure nuts on bolts in climbing situations? Seems like it may have potential, as I do see quite a significant number of loose nuts on bolts.
Not sure but there are possible implications with regards to hanger design where larger M12 nuts have come into contact with the carabiner gate as it is lifted.
It would need to be something slimline. Realistically persistent spinners need a dab of glue or something or replacement if the bolt is actually slowly withdrawing from the rock as I have seen in the past.
I like nylock nuts and have used them before where a bolt repeatedly takes multidirectional load leading to loosening. I take your points though about difficulty of removal and bolt rotation. Liquid nylock solution would solve the second problem and would allow you to use the compatible suplied nut rather than swap for a different nut.
It would be good if the nut could be found in this case to determine what caused the failure. Without the nut it's all just speculation.
Talking of speculation - could micro fractures develop in a nut which has been hammered (I tend to drive bolts in with the nut in place, so as to avoid hammering the unit in too deep) during bolt installation, which then develop concealed corrosion? Seems unlikely.
The correct torque doesn't particularly hold the hanger very tight to the rock, around 6kN is enough to move them on flat granite (hangers with dimples), there are also hangers available which are dished so they work like Belleville washers but the force to move them is the same.
When the bolt is highly loaded they all stretch, set and bend no matter which way you pull them, at failure the hanger is way off the rock like 10 or 15mm. They all fail in bending shear and the difference between the two pull directions isn't identifiable in the bolt when it fails.
Nylocks or thread lock are out, they can make re-tightening impossible, double-nutting is fine as long as it doesn't interfere with the karabiner. Hangers come loose and spanners are cheap!
Overtightening with rolled-thread bolts isn't instant death as some say, our 10mm wedge bolts take over double the given torque with no ill effects, over 90Nm they survive and the installing torque is 30Nm. With properly designed wedge bolts the protrusions on the clip which prevent rotation flatten and the whole bolt rotates rather than it breaking.
Dont people use nylocks on sport bolts? Or if just a normal nut, a spring washer on it?
It could be I'm misunderstanding the type of bolts used here, but this seems counter intuitive, and would seem to differ from the tests at a range of torque levels here:
I just watched that video, and I'm amazed they feel like they can deduce anything at all from those tests. Looked to me like almost every single pull-out happened at the strength limit of different parts of the poorly laid concrete slab, rather than the limit of the bolt. Indeed most of the bolts were still embedded in a hunk of concrete when they came up!
I agree that most appear to be testing the strength of their concrete and hence present no real insights about the effect of the torque level. However the zero torque bolt seemed to leave the concrete much more intact (and pulled out at a much lower force), implying that it was a different failure mechanism than the others (which would imply a difference)
Yes, those aren't wedge bolts that Europeans use they are the usual 5 piece the Americans use but they are slowly learning. None of the bolts in that video broke, the concrete failed below the requirements of EN 959 anyway. You should be seeing around 38kN for a 10mm bolt. Basically the video is meaningless.
Good to hear the voice of reason here Jim.
A nut which is finger tight doesn't unscrew by hanging on the bolt. It needs to rotate multiple times.
If the threads on the bolt are truly undamaged then the threads in the nut must have stripped or the nut actually snapped. Though not sure if that is even possible with the low forces involved in climbing falls/hangs.
A mystery, pity the nut wasn't retrieved.
The fastener will fail before the threads strip from the nut, the system is designed like that. I have actually snapped a nut in half testing a hanger design, took 9 tons pulling straight out though and not a mode of failure I've ever seen before in 50 years engineering.
As usual the report is a bit light on information, I went to look at a bolt where it was reported the nut came off, in reality the hanger had been loose for years and worn the bolt so far through that it broke. Another reason not threadlock the nuts, you can't pull the hanger off to see if the bolt is worn or corroded (and under the hanger is the danger region). Resin bolts are always the better answer and in 99% of the time can easily placed.
Interesting, I hadn't realised there was that much variation between non-glue in bolts. So for a non-tightened wedge bolt, would it be reliant purely on friction against the rock to hold, or is there some other mechanism?
I'd put my money on the nut and bolt being close, but not exact size matches.
Seems to be the only possibility left?
In reply to
the link is to a catalog of fixings, the page should open on Half nuts. Used to lock the half is the thickness in this case 2.2mm instead of 4.4mm this takes up no more room
As the nut and hanger failed by slipping off the bolt, this must have been at the end of bolt the fulcrum shear force increasing. is the bolt still good ?
> the link is to a catalog of fixings, the page should open on Half nuts. Used to lock the half is the thickness in this case 2.2mm instead of 4.4mm this takes up no more room
That's for the type of nut used in electrical distribution panels and is nickel plated brass.
RS also do these:
That's assuming that the extra thickness of a standard nut and the half nut don't cause fouling issues with the karabiner.
Also assuming that they work...
Sorry you missed the point
2 half nuts will build out no more than a full nut
the link was to show the principal half nuts available in tensile and SS
nb the locking is fixed without any extra turning on the bolt as highlighted as a problem above
> 2 half nuts will build out no more than a full nut
Standard practice is to use a standard nut and a half nut.
Which is what is stipulated in the link you attached in your subsequent post:
Stainless Steel Lock Nuts ( Half Nut ) A4 (316) DIN 439
Also known as half nuts, thin nuts or jam nuts
Tightened against a full nut to lock them both onto a thread
maybe some one will pop up to say 2 half nut can be used as A one Maybe you can throw some light? You said standard practice but rock bolts and lock nuts is not (yet) standard practice
more importantly I see the following
Jam nuts can be unreliable under significant loads. If the inner nut is torqued more than the outer nut, the outer nut may yield. If the outer nut is torqued more than the inner nut, the inner nut may loosen up.
Ether way it’s not a incident that will “hope “ lead to a knee jerk mass change of all fixed bolts
> maybe some one will pop up to say 2 half nut can be used as A one Maybe you can throw some light? You said standard practice but rock bolts and lock nuts is not (yet) standard practice
> more importantly I see the following
> Jam nuts can be unreliable under significant loads. If the inner nut is torqued more than the outer nut, the outer nut may yield. If the outer nut is torqued more than the inner nut, the inner nut may loosen up.
> Ether way it’s not a incident that will “hope “ lead to a knee jerk mass change of all fixed bolts
Eh? Except in special applications you put the thin nut on first, torque to half the required value then the standard nut and torque that to the full value. Means climbers have to carry two spanners though!
However this is useless on a wedge bolt so just nipping up the jam nut on the outside will do.
If I were to try using thinner jam-nuts under the usual nut, I presume I would actually have to tighten the jam-nut to full torque, to properly expand the bolt mechanism inside the hole, and then reduce the torque somewhat before fully tightening the standard nut up against the jam-nut.
Does that sound right, or might I have misunderstood or missed something?
In theory that's what you do but in practice who knows? The system is worked out on metal-to-metal joints and fastener stretch, the idea being the jam-nut underneath is in the end resting on the opposite flank of the thread compared to the load-bearing nut. Personally I'd just put the jam-nut on top and tighten to the reconmended 25% torque.
In reality I just whack the end of the threads so the nut can't fall off but can still be tightened if required, seems simple enough to me!
> Do you know if anyone has ever researched using a second nut as a jam-nut to secure nuts on bolts in climbing situations? Seems like it may have potential, as I do see quite a significant number of loose nuts on bolts.
With 12mm bolts and Fixé hangers or Petzl hangers which I use, even the nut with only 2 or 3 threads showing can snap a Krab so a double nutted bolt would be very dangerous I reckon.
I'm surprised they have knucles left using that spanner.
But is it the nut which gets in the way of the krab (in which case the amount of bolt protruding wouldn't matter) or is it the protruding bolt (in which case the number of nuts wouldn't.)
Probably all a bit hypothetical as I'm not aware of any of my nuts coming loose and I'm not in a hurry to change my practices when they seem to be working fine.
Some of the M12 through bolt and hanger combos used in Cumbria can be a pig for the krab getting jammed and generally fouled up. I think Jon has pointed out these problems local to him.
Often the thread on the bolt gets embedded into the krab , so its an awkward combination of krab, hanger, nut dimensions .
This rarely happens on M10. Maybe just needs a slightly larger / longer hanger for M12 bolts , not just a larger hole in an M10 hanger to call it an M12 hanger.
Fwiw, when placing through bolts , I tighten it up as much as I can , probably not car wheel stud torque when hanging off a rope using a standard length ring spanner.
This checks that the bolt collar is working properly. Then loosen off and just retorque to about 50 % of the previous maximum.
> Another reason not threadlock the nuts, you can't pull the hanger off to see if the bolt is worn or corroded
Surely someone checking bolts will be using a spanner which will easily shear the threadlock fluid? I've never known threadlock to completely seize a nut. As an aside, are you aware of threadlock exacerbating corrosion due to it trapping water?
. Resin bolts are always the better answer and in 99% of the time can easily placed.
> Fwiw, when placing through bolts , I tighten it up as much as I can , probably not car wheel stud torque when hanging off a rope using a standard length ring spanner.
> This checks that the bolt collar is working properly. Then loosen off and just retorque to about 50 % of the previous maximum.
Why? Where's the logic?
FWIW, car wheel nut torques vary between 80Nm and 180Nm for normal cars so hardly a standardised unit of torque and "standard" ring spanners don't exist either, only the head dimensions are in any of the standards, the length is unspecified.
For the common 17/19mm ring spanner pulling ca 15kgf on the end is the recommended torque for normal 10mm wedge bolts, tightening past that then slackening it is pointless.
> Why? Where's the logic?
> FWIW, car wheel nut torques vary between 80Nm and 180Nm for normal cars so hardly a standardised unit of torque and "standard" ring spanners don't exist either, only the head dimensions are in any of the standards, the length is unspecified.
> For the common 17/19mm ring spanner pulling ca 15kgf on the end is the recommended torque for normal 10mm wedge bolts, tightening past that then slackening it is pointless.
The spanner I take bolting is 200 mm long. 15kgf on this equates to 30Nm. The first hit on a quick google gives 30 Nm setting torque for an M10 through bolt on > 25 N/mm2 concrete, so this appears quite a plausible setting torque for rock.
However , I am on a rope placing bolts in a natural and variable material, rock.
The best I can do , apart from placing a bolt product glue in , is to assess the placement area, clean out the hole, then IMHO tighten the bolt fully with the 200 mm spanner , probably to c. 6O-80 Nm. This will proof test the rock around the placement for hidden flaws and set the collar fully. Slackening then tightening to 30Nm will hopefully hold the hanger snuggly without putting the rock under an unnecessary constant pre stressing load before it has to do its job of holding climbing falls.
It may be an over the top method but I like to think I am doing as much as practical to achieve a safe placement.
( regarding the reference to car wheel nuts, I was trying to give an example that climbers could relate to rather than using Nm. My berlingo is recommended at 100. )
I thought: when you torque the bolt the expansion element (sleevel / cone etc.) sets itself, but then if you undo the nut; the expansion sleeve / cone remain where they are - so you haven't really reduced the embedded load within the bolt and the rock......
Probably correct but I think the set stress will reduce slightly on the collar on slackening off.
The stress on the rock and bolt shaft will obviously reduce to zero on slackening off.
> But is it the nut which gets in the way of the krab (in which case the amount of bolt protruding wouldn't matter) or is it the protruding bolt (in which case the number of nuts wouldn't.)
I don't really know what you mean.
Jon knows what I mean. It's an issue with protruding bolts on 12mm hangers. The krab can get trapped between the bolt and the hanger and snap. Best to keep anything protruding to a minimum.
Hope he reads this and finds the link.
> Jon knows what I mean. It's an issue with protruding bolts on 12mm hangers. The krab can get trapped between the bolt and the hanger and snap. Best to keep anything protruding to a minimum.
This I believe is the photo that he posted at the time:
Think it's more to with the nut being too wide for the hanger as a result of replacing 10mm bolts with 12mm and not changing the hanger to suit.
30Nm gives the same load on the bolt and rock that the standard calls for ( in fact higher) so there's no point in going higher. In fact the cracked concrete torque is 40Nm so you might as well just go to that and leave it. The bolt doesn't mind.
> I'd put my money on the nut and bolt being close, but not exact size matches.
> Seems to be the only possibility left?
Except for the person who installed it saying otherwise further up the thread. (no pun intended)
Oh they did? Missed that. My bad. Skim read the thread.
> Think it's more to with the nut being too wide for the hanger as a result of replacing 10mm bolts with 12mm and not changing the hanger to suit.
How does that happen. Unless you drill the hanger out yourself?
Nobody makes different hangers for 10 or 12mm, just the holes are a different diameter, that's probably what was meant. A hanger would have to be enormous to avoid any interference witb all the different karabiners available and the fundamental problem is the draws are too light!
> How does that happen. Unless you drill the hanger out yourself?
Some 12mm petzl hangers I got about ten years ago appeared to be identical to their 10mm ones apart from the hole diameter.
Best just used on belays and not mid pitch.
I would humbly suggest that as the 10mm hangers rarely have krab hang up problems a few mm extra length to a 12 mm hanger might solve the issue .
Then the extra length makes it more likely they come loose......
> I would humbly suggest that as the 10mm hangers rarely have krab hang up problems a few mm extra clearance in a 12 mm hanger might solve the issue .
The problem isn't the hanger, it is unrestrained karabiner development. There are millions of bolts and hangers out there along with other items of climbing gear which are incompatible with some more extreme I-beam karabiners. A 12mm karabiner goes between the stud and hanger fine, offset the hole and you'll start getting problems between the nut and hanger with 10mm bolts.
The hanger and nut have been replaced. Don't know were the original hanger has gone but the nut will be buried in a drift of leaf litter somewhere down the bank.
The replacement hanger fits tight and snug against the rock now with adequate thread exposure protruding out of the chunky A4 M12 nut and is unlikely to move again. I would have to reject any notion of nut failure it this instance and put it down to a loose nut exploding off the end thread.
I am a great fan of the BP bar hanger and mourn the end of production and have been saving all the remaining stock for belays on harder low mileage routes as mallion/ring combos are unnecessary and unsightly in certain instances. The only down side with these hangers is they are slightly more susceptible to movement than a traditional plate hanger as there is less surface area and indeed flex to conform to uneven surfaces. So some may become loose jut like any other hanger but once they have ground their little niche they are undoubtedly the best. Just like a resin bolt they are gentle on krabs and can be threaded mid route.
Some people have said that resin bolts are easy and can be used 99% of the time. Of course they can but easy they are not and time consuming they are. Turn up at a shitty esoteric crag that has been neglected for 20/30 years with dubious or unknown access issues on a cold winters day. The rock is steep and short maybe 3 or 4 bolts long. Do you fly in there and do the deed or quadruple your time money and effort only to get banned or no one even shows an interest in your dirty little creation.
Check out all the horrible choss quarries in the Peak, they don't even use stainless steel in there. Not that I would stoop so low as to use non stainless kit but why would you when being chassed by security guards and dodging flying boulder. As least you can retrieve your hangers if it turns out bad.
Anyone have a metal detector to find the nut?