How to Choose Carabiners for Climbing and Mountaineering

Carabiners are a crucial element in the mountaineering safety chain and it is vital to choose them correctly. Here, we will explain the different types and their uses.

So many types of carabiners. Which to choose? Photo: Barrabes, Barrabes Team
Carabiners were invented by the Munich fire fighters in the 19th century.

Since then, they have been a basic and fundamental part of mountaineering. Can you imagine what climbing would be like, if carabiners didn’t exist?

As carabiners need to be lightweight and resistant, they are one of the most conflictive elements of the safety chain if we take into account the weak points of its design, such as the gate.

In this article, we’ll take a look at the following:

  • Firstly, the different types of gates with their pros and cons.
  • We will continue with the different locking systems, also with their pros and cons
  • We will look at the seven different types of existing carabiners according to their certification (which will tell us what they can be used for and, more importantly, what not to use them for, and why: climbing, belaying, via ferrata, etc.).

But first, some history.

It is not merely out of curiosity: looking back is fundamental to understanding the strength of a carabiner, why the standard is more lax now than it was a few decades ago and, more importantly, how the safety chain works as a whole, and how the climber forms part of it.

The evolution of carabiners and mountain equipment through time. Photo: JCIglesias/Barrabes

A Bit of History: Carabiner Strength


The first approved carabiners date back to the 1960s. In the absence of regulations, the UIAA (International Union of Mountaineering Associations) carried out the necessary tests and determined that the major axis strength of a carabiner should be at least 22kn, and its minor axis strength should be 11kn.

To meet this standard, manufacturers had to design heavy, remarkably large carabiners. The consequence was that most climbers and mountaineers continued to use non-approved, lighter carabiners.

After several years of no records of accidents caused by either approved or non-approved carabiner breakage, the UIAA decided to modify the regulations by lowering the required minimum minor axis strength to 9kn.

Reducing the specifications led to a reduction in weight and size, and this, together with the appearance of lightweight, durable 7075 aluminum, relaunched the use of approved carabiners. From this point, they began to be used on a massive scale.

Many studies later showed that the the impact force of a carabiner was limited by other components of the belay chain, such as the quickdraws, the dynamic elongation of the rope and the belay device and so the UIAA again reduced the minimum strength limit. As we will see, the specification for the most commonly used type B carabiners, is now 20kn (Kilonewton) for the major axis strength and 7kn for the minor axis strength.

In reality, this "downgrading" can be considered a consensus between standards, users and manufacturers: making a carabiner with guaranteed full strength in any situation would again lead to oversized and overweight carabiners that would make them inoperable, while the current strength is adequate for climbing use.

Why is it interesting to know this?

Although, if you use the right carabiner, it is extremely difficult to have an accident due to breakage and its strength is sufficient for any use, we should not forget that the original standard was limited in terms of strength by external factors, almost all of which are related to the dynamism of the belay chain. For this reason, we must be careful not to strain it.

In other words: part of the approval of the carabiner strength depends on our knowledge of how to manage the dynamic chain effectively. It is up to us. And this means it is essential to learn how it functions and how to do things correctly.

  • We should never expose ourselves to a factor 2 fall (the maximum possible in climbing).
  • We should always try to ensure that the possible fall is protected by a factor of less than 1.
  • We should try to ensure the belay is as dynamic as possible.

We insist: it is essential to understand this, because part of the safety of the carabiner falls on us. So if you don't know about fall factors (which is fundamental), we recommend that you take a look at the appendix of our article How to choose your climbing rope and mountain activities, where we explain this and other essential information on safety.

1. Gate Systems

There are basically three:

  • Wire
  • Straight
  • Bent

Traditional gates were straight, until the arrival of the first wire carabiners for mountaineering, at the beginning of this century.

What are their benefits?

  • They have the same strength as the classic systems
  • .
  • Up to 20 percent of the weight can be reduced during the manufacturing process. This can be used to make a lighter carabiner or keep the same weight and increase its strength
  • .
  • There is less chance of blockage caused by ice or dirt
  • The gate system is more durable, thanks to the elimination of the internal spring. More simple
  • It minimizes gate flutter and accidental opening due to impact against rock.
CAMP Dyon, wire gate carabiner

What is the dangerous gate flutter effect, and why is it eliminated with wire carabiners?

Gate flutter occurs when the carabiner undergoes vibration caused by the rope being pulled taught during braking. This vibration and tension generated opens the carabiner. It is not an everyday occurrence, but it may be more common than we think.

Because of their lower mass, wire trigger carabiners almost completely minimize gate flutter.

It also minimizes accidental opening due to rock impact.

Why are solid gate carabiners still being manufactured?

. Given the advantages of wire gates, why are the other systems still manufactured?

It is partly psychological (a solid gate transmits a greater sense of security, and some people prefer it), but it is also true that, cross loaded wire gates tend to deform and bend under a lower minor axis force (between 3kn and 4kn).

There is no risk of breakage, and it is not easy for this minor axis force to occur in normal conditions, but if it does, it is advisable to change the carabiner. Because of this, we can say they have lower durability, especially in sport climbing, where falls are constant.

And then there is the issue of the locking system: everything said so far about wire carabiners refers to type B (for climbing, quickdraws, etc.) Any other types, and any carabiner with a locking device, including type B, cannot be manufactured with a wire gate.

Bent Gates

Bent gates make clipping easier, but if the curve is very pronounced, it can be more prone to open accidentally.
Petzl Djinn Bent Gate

Carabiner Nose. Problem Solved

The elimination of the carabiner "nose" means modern carabiners no longer have the gate design problem that existed until a few years ago.

The gate would easily snag on your climbing gear when attaching and removing the carabiner.

Keylock, Wirelock...each brand has its own name and its own "nose" removal system.

Petzl Keylock system on the left, a classic nose system on the right

2. Locking Systems

It would be perfect if all carabiners had a safety locking system. It would completely avoid involuntary opening and the risk this poses when it hits the rock, flutter gate, whiplash, etc.

However, clipping, especially with a quickdraw, would be very complex if carabiners had this system, which is the reason they don’t.

For all other situations, safety locking gates should be used.

Broadly speaking, there are two systems:

  • Screw lock
  • Auto lock

There are several auto-lock systems that replace the screw-in system; practically every brand has its own design.

Some open with one movement, others require two or more (e.g., twist and pull), to increase safety and prevent the rope from accidentally rotating the lock and opening the system.

They all have one feature in common: as soon as you stop trying to open the locking mechanism, it returns to its original locked position. d

And this is the real benefit of auto-locking carabiners: they close by themselves. Unlike the screw-lock, you cannot accidentally leave it open, if you are in a hurry or just forget.

Something that is often confused should be made clear: many people think that the auto-locking system is designed to be opened more easily, and it is not unusual to hear comments such as, "I find a screw-lock easier than an auto-lock".

It is questionable, once you get used to it, if they are actually more complex to open, but this is not the purpose of the auto-lock design: it is manufactured to remain locked and closed, not to facilitate opening.

In short: the automatic mechanism refers to locking, not to opening, and that is why they are safer. They also eliminate the closing maneuver (which saves a few seconds, so think about this if you find them more uncomfortable to open). With a screw-lock the climber may leave it open to save on those seconds, whereas with an auto-lock, you can always be sure it is closed.

Screw-locks do not tend to get stuck due to cold, ice or dirt, which is something that can occasionally ocurr with the auto-locks. On the other hand, once you get used to them, auto-locks are more comfortable to use, as long as they are being held in your hand: an auto-lock hanging upside down from a belay point will be much harder to open than a screw-lock.

Edelrid Pure Screw Silver, screw-lock.
In recent years, some brands have focused on "different" safety systems, such as Grivel's twin gate. This has a double gate: the first one is lifted a little, and when you clip, both are released at the same time.

Once you get the hang of it, it is a very effective system, which can even be used with quickdraws on difficult placements with a lot of friction or if there is a risk of the gate opening, or a risk of falling.

But the most convenient system we know of, which is almost like using a carabiner without a safety catch, is the Edelrid Slider

The safety lock of this device is integrated inside the trigger and it has a small slider that is pushed down with just your thumb to unlock the opening. Of course, the slide returns to the locked position as soon as it is released.

You might think that grabbing the placed carabiner could cause it to accidentaly unlock. And it is true that it is easier to open by accident, but if you are careful, it is a truly extraordinary system for complicated situations, such as in alpine climbing,

This system also has another advantage: the carabiner weighs practically the same as a non-locking carabiner: 42 grams for the B-type carabiner and 60 for the HMS. That is a very noticeable difference compared to most locking carabiners on the market.

Edelrid Pure Slider -type B, left- and Edelrid Strike Slider -HMS, right-

3. Types of carabiners according to their use and resistance. Regulations.

What we have discussed so far is general for all types of carabiners. Now let's look at the different types and their uses. First, let's look at the applicable regulations and explain how manufacturers guarantee the resistance required.

The characteristics, typology and strength of carabiners is stipulated in the EN-12275:2013 and UIAA-121 standards on "Mountaineering and climbing equipment. Carabiners. Safety requirements and test methods."

It indicates the 7 types of existing carabiners according to the required use, together with the longitudinal (working) and transverse strength each of them must comply with, as well as the methods and tests they must pass to achieve this.

How do manufacturers guarantee the strength of a carabiner? The six sigma system

Leading and trusted brands use the Six Sigma system (process improvement methodology, focused on reducing process variability). The pioneers were the Welsh company, DMM, who continue to be a benchmark in terms of quality and use the 3 Sigma level within the methodology.

What does this mean?

Very briefly: since in any manufacturing process each sample will vary very slightly to the rest, if a quality control, from each manufacturing batch, chooses 100 samples at random, and the average resistance of those 100 carabiners is 20kn (which is the standard for a type B), what the control is really telling us is that in that batch there may be some above and others below 20kn, which is the average, and therefore there may also be carabiners that do not meet the standard in the batch.

If each carabiner manufactured were tested, it would be easy to eliminate those below this strength, but since quality control is carried out by statistical sampling, a system is required to ensure every carabiner in each batch meets the required strength

This is achieved by varying the manufacturing process using this methodology so that the worst of the samples is above the minimum required, so that all manufactured units meet the strength standard.

Of course, by raising the bar, it ensures the worst sample is only as low as the standard, so that most carabiners (those that in a normal system would meet the standard) now have a higher resistance: the one indicated on the carabiner is the one corresponding to the worst sample, the others are above it.

4. Types of Carabiners

1. Type B (Basic):

We could consider this a “universal” carabiner. It can be locking or non-locking.

Very versatile, very resistant, with a D shape that makes it easier for the rope to work on the longitudinal axis and avoid cross loading (the transverse resistance of a carabiner is much lower). Its symmetrical D shape has evolved over time to have a noticeably narrower bottom than the top.

Metolius Mini, D-shape asymmetric carabiner.
Nowadays they all have a more closed inner D section, and many are quite angled at the top. This avoids movements that could shift the force from the longitudinal to the transverse axis of the carabiner.

To avoid the decreased gate opening that occurs when increasing the angles, the most radical models add a small curve on the straight side of the D, to increase the space.

Due to its strength, and the fact that it tends to work on its main axis, this is the most recommended and commonly used type for climbing and mountaineering: quickdraws, 3-piece anchors, belay anchors, etc.

If used for quickdraws, it is recommended that they are not less than 10mm in diameter, to avoid premature wear due to friction.

On closure systems:

  • Non-locking carabiners are usually used during activity (quickdraws).
  • Locking carabiners are usually used for anchors, belays, 3-piece anchors, etc.
Grivel K1N Alpha, locking version
Regarding strength, the standard indicates the following:

  • Its major axis strength, with closed gate, cannot be below 20kn
  • Its minor axis strength, with closed gate, cannot be below 7kn
  • .
  • Its major axis strength, with an open gate, cannot be below 7kn
  • .

2. Type H (HMS, HalbMastwurfSicherung).

These carabiners were specially designed to be used with a Munter hitch knot for belaying or lowering maneuvers (HalbMastwurfSicherung means Dynamic Knot Belay).

They have an inverted pear shape, i.e., the gate and closed side form approximately the same lower angle with respect to the force axis, and the upper section is straighter, facilitating the correct functioning of the knot.

Type H are the most appropriate carabiner for belaying and rappelling, not only with a Munter hitch knot (which guarantees full and equal mobility on both sides of the carabiner), but also with belay devices and other semi-automatic devices used with double ropes, since the flat top section allows both ropes to brake and move equally as they run through the carabiner.

With other belay devices, where the rope does not need to run through a carabiner but only attach the device to your harness (e.g. a Grigri), a type D carabiner is recommended. The wide opening of an HMS biner is not necessary in this case, and the shape of the D carabiner helps prevent rotation, which can lead to cross loading.

They can also be used as a type B carabiner, but it is not recommended as they tend to move because of their shape and the rope runs close to the gate, or in a transverse direction which loses the force axis and, therefore, decreases its resistance.

The requirements for major axis and minor axis strength with a closed gate are the same as for type B, while a minimum of 6kn is required for the open gate major axis strength.

Due to their type of use, they have a locking system

You should always carry at least one for belaying, to get you out of an unexpected situation.

3. Type K (Klettersteig)

Designd for Via Ferrata.

The standard requires that it has:

  • A major axis strength higher to the rest (25kn compared to 20kn of type B). The carabiner has to resist impact when it runs along the cable to the anchor point in the event of a fall, so it has to be more resistant.
  • An automatic locking system (not screw-lock)
  • A greater opening angle, to be able to hook onto bars, etc. The standard indicates that all carabiners must have an opening equal to or greater than 15mm, except type K, which must have a minimum opening of 21mm. For this reason, this type of carabiner is oversized with respect to others.
CAMP Nomad, Via Ferrata carabiner: large opening, easy to use auto-locking system
The locking system has to be, for obvious reasons, automatic, and they are usually the most simple to use. It would not make sense if every change of lifeline required a complex maneuver.

Some are more simple, others more complex, with directional systems, etc. but the three mentioned above are the standard requirements.

No other type of carabiner should ever be used for via ferrata routes.

4. Type X

They have the same design as the first carabiners.

Oval and symmetrical. Today you can find models with a strength similar to type B, which even share the same standard, although the EN-12275 standard is less rigorous: 18kn major axis strength with closed gate, 7kn minor axis strength with closed gate, and 5kn major axis strength with open gate. This is why they are usually called "low load".

Why, then, are they still being manufactured and have not been completely replaced by B-type carabiners?

Because this design still has its niche: due to its shape, it is easier to use with pulleys, hoists, blocking devices, etc. (hence its use for work-at-height and industry). Since there are no angles, it is much easier to insert and extract and can be fully rotated (with the gate inverted), so it is also used for positioning material. It is widely used for aid climbing, for similar reasons.

We could summarize by saying that type X carabiners are for static or semi-static loads. Which would mean they can be used as connectors, but those with a lower resistance than that indicated by the type B standard should not be used as a substitute when there’s a possibility of great impact (e.g. as quickdraws).

5. Type T (Termination)

Directional carabiners incorporate a system that prevents them from turning, so that they always work in the correct direction.

The first models that were manufactured had a closed system. For example, if they were for quickdraws, the webbing was already placed inside its slot and it could not be removed or changed. But now, both the models used with quickdraws and those that cannot turn when belaying from the harness, are usually with a gate system.

Directional carabiners for quickdraws are less common because they can be replaced by removable systems such as the Petzl String, which converts any B-type carabiner used with a quickdraw into a directional carabiner, and because many quickdraws of all brands already come from the factory with a similar system installed.
Petzl String, attaches the carabiner to the sling converting it into a directional system
The minimum major axis strength for both open and closed gate is the same as a type B carabiner; however, since it is not possible for it to cross load, the standard does not indicate a minimum resistance for this situation.

6. Type Q (QuickLink / Screwlink).

Carabiners with no gate, with a screw locking system (not designed as a safety device, but as a locking system that supports the force). Traditionally manufactured in steel, although now there are also models in zicral (aluminum, zinc, magnesium)

Its industrial origin is made obvious by the polygonal shaped head of the thread, so that it can be tightened with a wrench.

They are inexpensive, very strong, and very durable, both because of the material (steel is approximately 10 percent stronger than 7075 aluminum) and the design (since they do not have a gate, once closed, they are practically a solid ring, with no weak points).

According to EN-12275, its major axis strength must be greater than 25kn, and its minor axis strength must be 10kn (the highest of all in the standard).

If they are stronger, more durable, and cheaper, why aren't they more widely used?

Basically, because their virtues become defects:

  • The higher strength means a higher weight. In terms of strength-to-weight ratio, aluminum wins by a landslide. If we used quicklinks instead of carabiners, we would triple the weight on the harness.
  • Due to its small design, with difficult to open and close screw-lock and with no gate to facilitate the use of the carabiner, they are very uncomfortable for use during activity. They are complicated to handle on most maneuvers, such as clipping to a hanger.

So, what are they used for?

  • Their low cost, which is much lower than that of a carabiner, and their high strength and durability, make them the best choice when you have to abandon gear on the mountain: e.g. an unfinished route, rappels without installation, and so on. This is the so-called “bail biner” use, for emergency or retreat situations.
  • They are excellent as a connecting system (actually, that's what they were born for: as a connecting system for industry, and for farmers). For example, for chains and multi-directional tensioned force systems.
  • D-shaped and triangular screwlinks have great value: they work triaxially, maintaining resistance in all directions. That's why they are used to join the straps of a chest harness.
  • They are very good long-lasting anchors. Not only because of their greater strength and durability, but also because it is not convenient to leave aluminum carabiners fixed on steel hangars: with movement, the steel wears down the aluminum and, in addition, as one metal is an anode and the other cathode, the aluminum will suffer galvanic corrosion.
Due to their low price, resistance as anchors, and triaxial loading capacity for use on a harness, they are widely used for work-at-height and caving. They are not needed for general mountain activities, but carrying a pair on your harness in case they are needed is highly recommended.

Steel Carabiners

Like the screwlink, steel carabiners are more durable and resistant than aluminum carabiners...but much heavier.

For this reason, they are rarely used as an individual safety element. But they are abundant in fixed installations on climbing walls: they appear constantly in the chain belay stations on sport climbing routes, overhangs, etc. They can withstand a long time before they have to be replaced due to wear and tear, and in addition, it avoids the possible galvanic corrosion that would occur if a steel hanger and an aluminum carabiner were left in contact for a long time.

Steel carabiner on a sport climbing, lowering chain.
Lately, Edelrid has designed some very clever carabiners, the Bulletproof are aluminum carabiners, with a steel insert in the area prone to rubbing. They weigh practically the same, but suffer much less wear in the exposed areas.
Edelrid Bulletproof Bent. Steel Insert

7. Type A

To our knowledge, only one carabiner has been manufactured with this system: the Kong Frog.

This system was designed by the Politecnico di Milano at the end of the last century, and has been marketed since by Kong.

It works automatically: it clamps on contact. Excellent for complicated clipping, in tough situations or out-of-reach hangers, etc.

The drawback is that if you need to A0, grabbing the carabiner in a hurry, you may inadvertently activate the release system.

Kong Frog. Type A carabiner.

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