Locking carabiners are an essential piece of climbing gear that continue to evolve as lighter designs and materials infiltrate the climbing protection market. While a few varieties are versatile enough to use for any purpose, most lockers, as they are commonly called, are now designed with a specific purpose in mind. There are lockers for belaying, rappelling, using as a master point of an anchor or at the end of a personal anchor system (PAS), and lightweight/compact lockers for building complex, equalized anchors for top-roping or on multi-pitch climbs. Below we will review the technical aspects and key factors in choosing a locking carabiner.
Why Use Locking Carabiners?
Locking carabiners, or just "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, lockers give peace of mind when 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––think 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, one relies on the security of a single carabiner. This is where a locker is preferred.
Most people's first locking carabiner is the one they buy for their belay device. A few are added to the rack for constructing top-rope anchors, and even more when they start multi-pitch climbing. You might only bring a couple lockers to the sport cliff, but it's not uncommon to have six or more on your harness when heading up a multi-pitch route.
Lockers come in many varieties. While some 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 HMS/pear or offset-D shapes, since they are versatile enough to do most things reasonably well. Experiment with different locking designs 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 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 like the most.
The shape of a carabiner is important to its function in a given application. Some can be used interchangeably with little negative effect, and others perform poorly at tasks they are not designed for.
The most popular style on the market, this shape comprises about 60 percent of the available carabiners produced. The offset-D features a wider basket that improves function, allows for a wider gate opening and can be scaled down resulting in smaller and lighter weight lockers. These carabiners effectively orient the load along the spine, so they are stronger then HMS/pear style, although not as strong as a traditional D-shape. All of the compact/lightweight lockers in this review are made in this shape, including the DMM Phantom Screwgate, Edelrid Pure Slider, and the Mad Rock Super Tech Keylock Screw. The only belay style locker that has this shape is the Petzl Freino.
HMS, or pear-shaped lockers, have a wide basket and a narrow crotch. HMS stands for halb mastwurf sicherung, or the half clove hitch belay. Most climbers know this as a Munter hitch. The Munter is a hitch that takes up a lot of space on the basket or the carabiner and needs to freely move without being pinched by the spine, hence the wide basket. These are also used frequently as belay and rappel carabiners, since they allow for even feeding of brake strands without pinching because of the wide, symmetrical basket used. For this reason they are the most common first locker purchased by new climbers, and are the second most frequently used shape of locker. HMS/pear shaped lockers are possibly the most versatile, as they are capable of doing anything, but they are usually rather large, and tend to be heavier than Offset-D carabiners because their design is not as inherently strong, requiring more material to compensate. So while they can be used for any locking purpose, most climbers only use them on their belay or rappel device, or as a master point of an anchor. Six of the lockers in this review are made in this shape, including the Petzl Attache, Black Diamond Vaporlock Magnetron, and the Edelrid HMS Bulletproof Triple FG.
D-shaped lockers are not very popular anymore, but are still produced by climbing companies. The standard D is the strongest carabiner design because it keeps the load oriented along the strongest axis (the spine), but is a poor performer at many other common climbing tasks due to the tight basket and crotch shape. These carabiners aren't really used for climbing much anymore, having been pretty much totally superseded by the Offset-D shape, so we didn't include any in this review.
The oval is the original carabiner design, and the oval shaped locker is still produced by some companies. While there are certain benefits to the oval shape, like being able to fit a lot of gear onto it, the shape is inherently weaker than others since the load is not directly in line with the spine, and does not have as wide an opening or useful basket as Offset-D or HMS lockers. We did not test any true oval locking style carabiner shapes.
Gate Closure Style
Locking carabiners are often described as being double-action or triple-action. The number of actions refers to how many separate movements are required to open a locked gate. A non-locker is single action, requiring only one movement, that of opening the unlocked gate. A screw gate locker is a double action, requiring you to unscrew the locking mechanism, and then open the gate––two actions. Standard twist gate auto-lockers, like the one found on the Petzl Freino, are also double action. Triple-action lockers, such as the Edelrid HMS Bulletproof Triple FG require three actions, in this case slide, twist, and then open. Below we briefly describe the four styles featured in our review, which does not represent all styles of locking carabiner closures out there.
This is by far the most popular style of gate closure system. The screw gate relies on a small metal cylinder which screws up and over the nose of the carabiner, preventing the gate from being opened. Some designs, like the DMM Belay Master 2, use an additional closure that further prevents the screw gate from opening. The downside to standard screw gates is that they must be manually closed each time, something climbers often are forgetful about. For this reason, Petzl put a red stripe along the gate of the Attache to indicate whether it is closed or not — "See red, you might be dead!" Most of the lockers we reviewed, and use, are screw gates.
Twist gates, such as on the Petzl Freino, can sometimes be more cumbersome to open, but the locking mechanism is automatic once released, thanks to an internal spring, making for a potentially more user-friendly tool, especially when used with belaying. The moment the gate closes, the 'biner becomes locked, adding an element of gate security due to the fact that it is impossible to forget to lock them. The downside is that when trying to remove them from places that don't need them to be locked, such as a gear loop on your harness, they are still locked and need to be manipulated in the right way to get open.
Black Diamond makes auto-locking carabiners that use small magnets on either side of the nose to hold the gate closed. We tested the Vaporlock Magnetron, but they use this technology in a few other types of locking carabiners as well. To open the gate, simply depress the lever armed triggers on either side of the gate, and then open. This is a double-action design that does not use the common twisting mechanism, and is also auto-locking upon closure, so there is no need to remember to lock the gate. This system is surprisingly simple to get used to, but does have the downside of the magnets attracting ferrous material if left in the dirt, becoming sticky or sometimes clogged. Also, when used in cold and icy conditions the gate is more likely to freeze shut than others, and depressing the triggers can be more challenging with thick padded gloves on.
The Edelrid Pure Slider uses a small, sliding locking mechanism that hangs up on the nose of the carabiner when the gate is closed, and is easily slid down the shaft of the gate with one finger before opening. While it is a double-action auto-locker, it is a bit less secure than the others tested because it is so incredibly easy to slide open the small locking mechanism. However, for this same reason the Pure Slider is a good fit for the end of quickdraws or slings where you want a little extra security, but can't stop to fiddle with locking a regular locker.
There are two different shapes of carabiner noses: keylock and nose-hook. In the history of carabiners, keylock noses were invented relatively recently (although have still been around for over 20 years). They are widely regarded as superior in design because they have no hook that can catch on bolts or slings, and are therefore easier to clip and unclip quickly. All of the lockers tested for our review have keylock noses. Nose-hook shapes have largely been relegated to use with wire gate offset-D shaped carabiners, usually on the end of lightweight quickdraws.
Type of Metal
Locking carabiners are made out of either steel or aluminum. Steel carabiners are very durable, and are becoming ubiquitous as the 'biners on the end of fixed draws at sport cliffs or in gyms, or the lower off 'biners left at the top of climbs at popular areas. These uses are common for non-lockers; steel lockers are generally more expensive, stronger, and weigh a whole lot more than their aluminum counterparts, to the point where there is no reasonable climbing application. 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 come either with a burnished metal finish, or are available with an anodized finish. Anodizing is a very thin layer applied over the entire surface of the carabiner, making the finish feel smoother, and allowing for different colors, which can help differentiate carabiners on your harness. The Edelrid Pure Slider and Petzl Attache are both good examples of anodized locking carabiners. Beyond cosmetics, 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.
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 become the most common, 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. I-beam carabiners are also 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 will last longer.
Locking carabiners are forged either through cold forging or hot forging processes. Both produce lockers that are strong and durable, though each process has its own benefits. The cold forging process is the traditional way carabiners have been produced, by taking a piece of aluminum and bending and stamping it with no additional heat applied.
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 Slider. 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 done 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 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 this 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
The 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, called "cross-loading." 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 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 much into your decision. 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 lightweight lockers like the DMM Phantom Screwgates.
Worth mentioning is that like most pieces of gear, there is an obvious trade off in weight and size. 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 Mad Rock Super Tech on protection or bolts, and bring a couple larger, more versatile lockers like the Black Diamond Vaporlock Magnetron for anchoring in or belaying.
Knowing about the different shapes, construction styles, gate styles, and strength helps you be confident in the performance of your climbing gear. In the end, the correct locker for the job will depend on what you intend to use it for as the first consideration, followed by weight, price, and quantity you intend to purchase as secondary considerations. We hope this article was helpful in your search for the best locking carabiners, and be sure to check out our full review for our top recommendations.