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How to Choose the Best Locking Carabiner

Black Diamond Rocklock Twist Lock
By Ryan Huetter ⋅ Review Editor
Wednesday November 16, 2016

Locking carabiners have evolved a lot in the last decade. They are lighter and are designed for more specialized tasks. There are few one-size-fits-all carabiners. Instead, there are certain carabiners that are best for belaying, rappelling, use in anchors and lightweight biners. Below, we look at key factors to use when choosing the best locking carabiner.

Why Use Locking Carabiners?

Locking carabiners, or lockers for short, are in integral part of a climber's kit. Whether you are a beginner gym climber who just passed their belay test, an El Cap veteran building anchors for hauling heavy loads or a lightweight alpinist climbing routes in the mountains, locking carabiners give us piece of mind when we are constructing safety systems that may rely on one single piece of gear. While non-locking carabiners are used in greater numbers in a typical climbing setting, in the form of quickdraws or cams clipped with a single carabiner, they are part of a system that implies redundancy. But when doing things such as attaching the belay device to your harness, building a top rope anchor or clipping into an anchor with a personal tether, and you are needing to place a lot of faith in just one carabiner, that carabiner should be a locker.

Many people's first locking carabiner is the one they buy for their belay device. A few get picked up for constructing top rope anchors, and even more when they start multi-pitch climbing. You might only bring a couple of locking carabiners to the sport cliff, but have 6-10 on your harness when heading up a multi-pitch route.

Lockers have come a long way in design and construction, and now come in many varieties. While some of these locking carabiners can perform all tasks reasonably well, there are others that are better suited to specific uses. When first buying lockers, it can help to stick with generic shapes like the offset D and pear shape, since they are versatile enough to do most things reasonably well. Experiment with different gate closure styles to see what works best for you in given situations, and then as you build up your kit more, you can diversify into some of the more specialized carabiner offerings. Read on to find out more about the different aspects of locking carabiner design and construction, and then head to our Best Locking Carabiner Review to find out which we liked the most.


Type of Metal

Locking carabiners are made either out of steel or aluminum. Steel carabiners are very durable, and are appropriate for use in climbing situations where there is a lot of abrasion (like top rope anchors in desert environments where your rope gets quite gritty). Steel lockers are generally more expensive, stronger, and weigh a whole lot more. Aluminum locking carabiners are lighter, are made in a greater variety of shapes and weights, and are a good choice for the majority of climber's needs. All of the locking carabiners reviewed here are aluminum construction.


Aluminum carabiners either come in a burnished metal finish, or are available with an anodized finish. This comes in the form of a very thin layer being applied over the entire surface of the carabiner. The anodized version allows the carabiner to be dyed different colors, which can help differentiate carabiners on your harness. The Edelrid Pure Screw and Petzl Attache are both good examples of anodized locking carabiners. Beyond being purely cosmetic, however, anodized lockers are more impervious to the types of corrosion found in marine environments. Salty sea air reacts poorly with aluminum and can corrode the material, so if you climb regularly near the ocean, or if you take a climbing holiday to a place like Mallorca or Thailand, keep the corrosion in check by washing your gear regularly.

Stock Shape

The stock of the carabiner refers to the shape of the material that it is made out of. Common stock shapes include round, oval and I-beam. The less material that the stock is made from, the lighter the carabiner's weight will be. I-beam stock construction has really taken off in recent years, and is allowing carabiners to be produced at competitive strengths at a fraction of the weight.

Weight is not always the final consideration though; as the stock shape goes from round towards I-beam, the radius will decrease. This decreased radius will make the rope turn sharper when clipped into the locker under load, and will result in an increase of friction. When using a belay device in plaquette-mode, such as the Black Diamond ATC Guide, this increase in friction can make for a more tiresome belay. The round stock found on the Black Diamond RockLock Screwgate was kinder on our elbows during long belays.

Narrower stock shape such as found on I-beam carabiners also are less durable when handling abrasion and friction. If choosing lockers that will be on the rope end of a top rope anchor, solid round stock carabiners are the better choice.

Forging Process

Locking carabiners are forged either through Cold Forging or Hot Forging processes. Both produce locking carabiners that are strong and durable, though each process has its own benefits. The cold forging process is the tradition way carabiners have been produced, by taking a piece of aluminum and bending and stamping it with no additional heat applied. The Omega Pacific ISO Locking Standard D is a good example of the traditional cold forging method.

Hot forging is when both the rod stock and forge dies are heated prior to working, a process that allows for the creation of more intricate shapes such as the Edelrid Pure Screw. Some users have complained about the lack of durability in hot forged shapes, this is likely due to the inherent decrease in metal used in the creation of many of these more sculpted designs.


All of the carabiners in this review are tested to the CE, UIAA or ISO standards, and often a combination of more than one. What does this mean to climbers looking for quality safety gear?

CE is a safety standard designated by the European Union and is required to sell climbing gear within the EU. The CE does not itself test gear-that is done by independent labs, or invent the standards, which is does by the UIAA.

The UIAA is a climbing organization that has been around since 1932, and establishes the safety standards we see in our climbing equipment. The CE often uses their recommendations, though in some instances the UIAA standard is stricter than the CE equivalent.

ISO testing refers to a quality control standard that is followed by manufacturers to assure that each product comes out above a given standard. This is a company rating rather than an individual product rating, so a carabiner like the Omega Pacific ISO Standard Locking D will still carry a CE certification in addition to the ISO designation.

What's in a kN?

A kilo newton (kN) is the standard unit used to describe force, and is equivalent to about 220 lbs. The CE and UIAA standards include minimum strength requirements for carabiners that hold their certifications, and these designation should be laser etched or stamped into the side of any carabiner that you use for climbing.

The strength of a carabiner depends on the axis that it is loaded in.

Major Strength Axis

is in line with the spine, with the carabiner being pulled simultaneously from the basket and the crotch. This is the strongest orientation, and requires a minimum 20kn breaking strength.

Minor Strength Axis

Is perpendicular to the major strength axis, and is when the carabiner is pulled against both the gate and the spine. This is not the way carabiners are designed to be used, but it is not uncommon for a locking carabiner to rotate and become loaded, especially when belaying. This is a weak orientation, to be avoided, and requires a minimum of 7kn breaking strength.

Open Gate Strength

Refers to the carabiner's strength when loaded with a gate open. This can occur when a locking carabiner is improperly locked, or when it is inadvertently pinned and opened against the rock or other material. The open gate strength standard is 7kn for D and Offset D shapes, and 6kn for HMS/pear shapes.

Size and Weight

If you are looking to buy your first locking carabiner for belaying or rappelling, then size and weight should not factor in to your decision too much. In fact, having a larger gate opening, and a heavier, more durable stock will result in a better performing carabiner in these uses. Once you start to climb longer multi-pitch routes, or are venturing farther into the mountains where weight begins to matter, then weight and size start to play a bigger role in deciding which carabiners to bring along.

Full sized, round stock lockers like the Black Diamond Rocklock Screwgate are great for belaying and building anchors, but put 6-8 of them on the back of your harness and you will notice the weight a lot more than the same number of Petzl Attache lockers.

There is an obvious trade off in weight and size though, and so don't expect the same lifespan out of your lightweight, I-beam carabiners as you might out of something with a thicker, heavier stock. A good comprise when building up your multi-pitch climbing anchor kit is to use compact, ultralight lockers like the Edelrid Pure Screw on protection or bolts, and bring larger, more versatile lockers like the Mad Rock Ultra Tech HMS for anchoring in or belaying.

History of the Carabiner

Rock climbing and mountaineering has roots dating back into the 16th century, although with marked differences from the current sport. Often the earliest climbs, like the first ascent of Mount Blanc in 1786, were done by the most obvious path to the summit. These early mountaineers would follow the path that provided the most walking terrain. Still, these climbs often came with grave consequences and were not without their technical challenges. By the late 1800s there were many different mountaineering groups spread across Europe. Often many of these groups would hold meetings at their local cliffs or boulders, like the boulders strewn about the forests of Fontainebleau outside of Paris, France. Here these early mountain climbers would practice their climbing skills in order to prepare for the Alps and other big mountains.

It is hard to imagine a time before many of the modern tools that we use in rock climbing but there was indeed a time before even the simplest items like a carabiner. In fact, the name carabiner dates back to 1800 and the Napoleonic Wars where it stems from the German phrase "karabinerhaken," which translates to "snap hook." The snap hook in reference was one being used to connect a carbine rifleman's bandoleir to his carbine rifle. These snap hooks were also used by the "Carabiners," as they were called, to affix various items to their belts and bandoliers. Through the years the name of these rifleman became associated with the snap hooks they used.

By 1868, an official patent for these snap hooks surfaced. The item was a metal oval, most likely made of steel, that had a gate that could be opened outwards and then pushed closed. The patent labels the biner as a "ring hook" and it was most likely intended for connecting chain or tied rope together. By 1897 another patent appears, this time referred to as a snap hook. This hook slightly resembles a modern day biner but has a second connecting point, a closed metal ring, affixed to the top of an oval with an openable gate (imagine a biner with an extra circle attached to the end).

By the late 1890s, another patent showed up for a tear-drop-shaped snap hook that has a small piece of metal inserted over the gate arm. This piece of metal has threads on it and can be screwed up to block the gate from being opened. It is here that we see the first locking carabiner.

In the early 1900s, mountaineers had limited ways for connecting themselves and their rope to a piece of protection. At the time the majority of protection for rock climbing was created by tying a rope around a block wedged in a crack, known as a chockstone, or by tying off flakes or horns of rock. When the climber would tie off one of these points they would tie the protection rope around their rope in order to catch them should they fall. Around this time climbers had begun to create and utilize the very first pitons, metal wedges to be hammered into cracks for protection. However, with the advent of pitons and their popularization as the best form of protection, climbers needed a way to connect their rope to their pitons, and so the carabiner became a part of the rock climbers' tools.

It was around 1911 that a strong German rock climber and mountaineer named Otto Herzog was pushing the limits of climbing in the Alps. Herzog was a strong proponent of using pitons while climbing and mountaineering and is often credited as being the first person to use carabiners in a climbing system. Herzog used these biners to clip his rope to his pitons so that should he fall they would catch him. It didn't take long for this to become the method of choice for climbing protection. By 1921 a company based in Munich, Germany began to produce the first biner specifically for climbing, it was made of steel and at 130 grams weighed nearly six times as heavy as a modern day biner.

During the second World War the US government began to outsource the production of many different high demand items that could be made in different shops across the nation, from textiles to metal products. Many different circular stock aluminum carabiners showed up during these years made by various companies and then stamped with a generic US label. In the post-war era many of these biners, pitons and tools came into the hands of the ever growing sub-culture of rock climbers who were striving to tackle bigger, harder, and more technical objective across the nation and around the world.

Many of the early American climbing legends in the United States started their climbing careers with military issue pitons, biners, and fabric goods like duffle bags and backpacks. In 1957 one of these climbers, Yvon Chouinard, had recognized both a need and a demand for improved climbing-specific hardware, so he purchased a second-hand forge and began manufacturing a new line of pitons and carabiners and then selling them out of the trunk of his car. These new lighter and stronger carabiners and the various sizes of pitons played a major roll in revolutionizing the rock climbing game and opening a world of big wall climbs like those on the massive granite walls in Yosemite Valley.

Over the next 30 or more years, the carabiner continued to see many improvements and modifications. Many different screw gate models were introduced and in the late 1970s the first auto-locking biner was prototyped by Salewa. During these years the biggest modifications were in the different construction patterns and, most importantly, the different types of metal alloys that were used. Companies have since embraced high tech methods for forging metal to create incredibly light weight and amazingly strong biners, often weighing less than one ounce, or 28 grams, and holding as much as 7500 pounds or more. So today we can be thankful that we don't have to carry dozens of 130-gram steel biners with as many heavy iron pitons!

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