Mountain Project Logo

Is 6kN really the magic number?


Original Post
Hobie Ponting · · Stamford, CT · Joined Dec 2016 · Points: 1

A friend and I took an three day Trad Fundementals course a few years ago with a guide down in WV. He was explaining the gear rating system and in the process told us that anything under 6kN should only be used for aid climbing. I understand the math behind fall factors and forces but have never been able to find documentation on gear ratings for aid vs. free climbing. Obviously it all comes down to forces not aid v free but wanted to hear what other peoples limits are on gear ratings.

Gunkiemike · · Unknown Hometown · Joined Jul 2009 · Points: 2,800

There's no hard-and-fast cutoff. 6 kN is pretty much just his opinion and/or personal take on what he's comfortable with.

Mike Byrnes · · Unknown Hometown · Joined Nov 2016 · Points: 0

I’ve taken about a 20ft fall on a 5kn piece. They still do the job, just a little spooky 

Christopher Smith · · Unknown Hometown · Joined Jan 2017 · Points: 0

You are usually only going to see falls close to that number low down on a climb when the FF is still rather high (of course with the caveat of climbs were your rope might go tight against a rock in a fall reducing the amount of rope actually in play during the fall).  That said I've had a friend that took probably a .8 FF fall on a X4 .1 before which is only rated to 5kn.  I know BD only really says that their C3 000 is an aid piece as far as cams go and it's rated to 4kn.  So it seems at least as far as BD, that the industry cutoff is 5kn.

bkozak · · Sterling, VA · Joined Jul 2016 · Points: 70

In the "Boys in the Bugs" video, Will Stanhope takes a huge whipper onto a size 0 mastercam, which is only rated to 5 kn.

John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,535

Anything at or below 6kn, you'll want to double up if you can. The strength rating really isn't at issue, but more the size of the gear means the margin of error is small enough that the gear is marginal no matter what. 

Porter McMichael · · Bellingham, WA · Joined Jun 2017 · Points: 30

I'll take a 4 or 5kn piece over nothing at all. At the worst it'll break my fall a tiny bit before my next piece. Besides, pieces that size, especially nuts, weigh practically nothing. I feel like kn ratings aren't super relevant, you place what fits best, and if its a tiny piece, you climb extra careful!

Jeff G. · · Fort Collins · Joined Feb 2006 · Points: 927

I've never understood the "free vs aid" piece.  All pieces can be used for free climbing.  Maybe you shouldn't whip 30 feet on a #2 rp but it can certainly hold a fall when placed above your head or at chest level.  Often times that's what you need for the crux moves.  Silly to think you wouldn't bring the smallest gear needed because it might not hold a big fall. 

King Tut · · Citrus Heights · Joined Aug 2012 · Points: 430

They, in a bit of corporate covering of asses, are just telling you the piece won't hold a FF2 (worst case scenario, but possible).

Very, very few falls are that severe.

And whether the rock such a small piece is placed in will hold is a significant concern too.

So don't try to make a living taking whips onto small gear, but everyone is gonna take what they can get.

Christopher Smith · · Unknown Hometown · Joined Jan 2017 · Points: 0

https://www.youtube.com/watch?v=j63aJbzgORk

Some falls on 4kn rated 000s at the end of this video.  Granted they are pretty low force swings with a really soft catch.

· · Unknown Hometown · Joined unknown · Points: 0

You might want to ask for a refund he meant 5kn. All the gear for climbing had to pass the 5kn test to get certified as gear meant for fee climbing. Aid is a different stories. Including open gate carabines. 

Sean Onasch · · fort collins · Joined May 2016 · Points: 115

I took about a 10ft whip on a 5kn nut a couple months ago and it held no problem. 

Tomily ma · · Unknown Hometown · Joined Jan 2011 · Points: 305

I fell on a number 2 bd nut. A small fall but I was still shocked it held. 

Eli . · · GMC3500 · Joined Nov 2010 · Points: 3,199

A friend and I broke a 2.5kn nut from whips. It still held about 4 solid lead falls before snapping. I think that there is no cut off, but 6kn is definitely safe.

Chalk in the Wind · · Unknown Hometown · Joined Aug 2014 · Points: 3

It seems that most gear manufacturers state that 4 kn and lower is aid-only. In reality, that probably means you can safely take a lead fall on that or a little lower, assuming the placement and the rock are good, as they for liability reasons are never going to say the real bottom line is below the suggested one.

As others have said, back up that tiny piece or get another in ASAP unless you are on no-way-am-I-gonna-fall terrain.


DrRockso · · Red River Gorge, KY · Joined Sep 2013 · Points: 356

If it's all you got then you place it... as John said, doubling up if possible.

Robert Michael I would contend this is one of those things that gear manufacturers aren't being super conservative about. It would be easy to generate a fall of 4+ KN, and that's assuming you have a textbook placement in bomber rock. It would be risky to trust aid stuff on a climb you think you are likely to a high factor fall on. Maybe the actual breaking strength is a lot higher than the manufacturer rates, I doubt their is a ton of cushion built in though, those wires are slim!

Jim Titt · · Germany · Joined Nov 2009 · Points: 490

The certification requirement for nuts is 2kN and for cams 5kN, anything below this is only to be sold for progression (aid). That said, anything above 6kN is unlikely to break in a lead fall, anything below might.

David Kerkeslager · · New Paltz, NY · Joined Jan 2017 · Points: 138
Jim Titt wrote:

The certification requirement for nuts is 2kN and for cams 5kN, anything below this is only to be sold for progression (aid). That said, anything above 6kN is unlikely to break in a lead fall, anything below might.

I'm curious about how these numbers were chosen. I'm not disagreeing with you, I'm just trying to get an idea of how well the data these numbers come from represent real life use cases.

My ideal experiment would be to give a bunch of climbers a bunch of load cells and have them trad climb for a month with load cells on all their gear, tracking the forces/fall-factors of all their falls, but obviously the cost of the load cells alone would be cost prohibitive. :D

King Tut · · Citrus Heights · Joined Aug 2012 · Points: 430
David Kerkeslager wrote:

I'm curious about how these numbers were chosen. I'm not disagreeing with you, I'm just trying to get an idea of how well the data these numbers come from represent real life use cases.

My ideal experiment would be to give a bunch of climbers a bunch of load cells and have them trad climb for a month with load cells on all their gear, tracking the forces/fall-factors of all their falls, but obviously the cost of the load cells alone would be cost prohibitive. :D


No, all you need is a test rig and someone to right down the numbers to find the rope's max impact force.

If a rope is rated for say, 8kn max impact in a FF2, then any factor 0.5 and below will only be 2kn etc. This is most leader falls when there is a significant amount of rope out (napkin math).

David Kerkeslager · · New Paltz, NY · Joined Jan 2017 · Points: 138
King Tut wrote:


No, all you need is a test rig and someone to right down the numbers to find the rope's max impact force.

If a rope is rated for say, 8kn max impact in a FF2, then any factor 0.5 and below will only be 2kn etc. This is most leader falls when there is a significant amount of rope out (napkin math).

That gives you the force given a certain fall factor given a static mass drop, but that's not really the question I'm trying to answer. I want to know when pieces actually fail in practice. Fall factor is one component in that, but there are a lot of other components (dynamic components besides the rope, such as the climber and their gear flailing; placements failing due to things other than the piece breaking, such as rock breaking). In some cases (i.e. brittle rock) fall factor might not even be the most important number. I suspect that actual falls are complicated/variable enough systems that they can't reasonably be modeled, but I don't know of enough empirical data on actual falls to even be confident of that.

There's a ton of experiential evidence on this, but that succumbs to all the normal problems of experiential evidence (confirmation bias, climbing only on certain kinds of rock, etc.). I like numbers. :D

That said, I'm not hopeful my ideal study will happen any time soon. Like I said, it's cost prohibitive.

King Tut · · Citrus Heights · Joined Aug 2012 · Points: 430
David Kerkeslager wrote:

That gives you the force given a certain fall factor given a static mass drop, but that's not really the question I'm trying to answer. I want to know when pieces actually fail in practice. Fall factor is one component in that, but there are a lot of other components (dynamic components besides the rope, such as the climber and their gear flailing; placements failing due to things other than the piece breaking, such as rock breaking). In some cases (i.e. brittle rock) fall factor might not even be the most important number. I suspect that actual falls are complicated/variable enough systems that they can't reasonably be modeled, but I don't know of enough imperical data on actual falls to even be confident of that.

There's a ton of experiential evidence on this, but that succumbs to all the normal problems of experiential evidence (confirmation bias, climbing only on certain kinds of rock, etc.). I like numbers. :D

That said, I'm not hopeful my ideal study will happen any time soon. Like I said, it's cost prohibitive.


There is a ton of anecdotal evidence on this and virtually no empirical data to my knowledge.

Small gear rips out more often due to rock breaking, material deformation of the gear, movement of the gear when climber moves past it and climber error placing it (to name a few).

All the makers can do is give you a number the gear could hold in an ideal situation.

However, one of the top causes of accidents is small cams ripping out of cracks most likely due to bad placement/rock quality. In this sense the quality of the placement and good judgment as to whether it is fall worthy is more important than any rating by a maker as to what will break the gear.

Guideline #1: Don't be a jerk.

Climbing Gear Discussion
Post a Reply to "Is 6kN really the magic number?"

Log In to Reply