Note: The spellings of carabiner and karabiner will be used interchangeably in this essay. Both are appropiate spellings.

From founding Alpine Training Services, being a climbing instructor for 15 years, founding the “West Coast Canyoneering Method”, and spending the last 23 years as a recreational climber, canyoneer and mountaineer I can tell you one thing for sure- the sum total value of all your gear is not worth your life! Don’t hesitate to leave it all behind to bail a route, canyon or mountain! That being said…

What is a Carabiner?

A carabiner is designed to be a strong connecting link used for joining material (ropes, hardware, slings, etc.) together to create life safety systems in a primarily vertical world. Today’s aluminum carabiners have an incredible “strength to weight ratio”. When the right carabiner is used for the right application much can be expected. However, when misused a carabiner can become incredibly weak! Due to the dynamic nature of vertical risk adventure sports, redundancy (when possible) is the key to success. Systems that lack redundancy should be viewed as less dynamic and greater care should be taken during the design and execution of the skill sets applied to these types of systems. Please read on to get a better understanding of the most basic link in the dynamic and static systems rock climbers, canyoneers and mountaineers use all of the time.

A Short History

The word carabiner is actually short for "karabinerhaken", meaning "hook for a carbine" in German. Carbine hooks are oval-shaped devices used for ropework in the shipping industry. For considerations of the modern form of karbiners, we need to jump to World War II. Steel links were created with spring loaded gates that were designed to lock paratroopers into tag lines aboard airplanes.  The paratroopers would then jump from the planes into the battle below. Steel was the primary material used for these oval shaped links.   

Since early carabiners were made of steel, the carabiners had a low strength to weight ratio, (meaning strong but heavy).  Today the carabiner designed for rock climbing, canyoneering, mountaineering, etc. is made of aluminum.  Though not as strong as most steel carabiners, the aluminum carabiner is cold forged and has an incredibly high strength to weight ratio.  The aluminum carabiner is designed not to fail when the right carabiner is selected for the right application. The break thru of aluminum technology has allowed the forward progress of newer, more complex equipment that has increased the safety margins dramatically in these vertical sports.  This increased safety margin is one of the primary comparative reasons that high angle activities have become so popular over the last few decades.

The Carabiner Family

Even though there are dozens of different shapes and sizes of carabiners there remains a few similarities that we should review before we get started with the differences.

Carabiner Strength Ratings

Carabiner strength ratings were at one time measured in foot pounds.  Now carabiners are rated in kilo-Newton’s or “kN”.  A kilo-Newton is a measurement of force. Since most of what we do in the vertical world involves dynamic movement, (which creates energy that is converted to a force on an object), it makes better sense to measure the strength of our equipment with a rating of force it can withstand.  

Basically –

A KiloNewton is 1000 Newtons which is equal to roughly 224.8 pounds. A Newton is a metric unit of force that when applied to one kilogram mass would experience an acceleration of one meter per second per second. (Kg m /sec²).

The basic average on strength for the equipment recreational climbing companies are manufacturing is a minimum breaking strength (MBS) of around 4950 lbs. 

Markings on Carabiners

When used properly these system links are incredibly strong! However, because we are dealing with dynamic forces and its multipliers it is very easy to “misuse” a carabiner.

Take a look at the spine of almost any carabiner. You will see several markings. The numbers listed here should be in kN for any modern day carabiner.

Major Axis Loading

This rating is based on a load that is pulling along the spine from either end. For example: a bolt to webbing, a stopper to a rope, webbing to webbing, etc...

Cross Loading

The next rating is a cross loaded rating. This number will be significantly less as the carabiner is not designed to be loaded in this manor. At the base of the gate you will see a small hinge pin. When load is applied to a cross loaded carabiner, this hinge pin is the first to go; once sheared the gate will swing out backwards, thus failing the carabiner.

Open Gate Loading

The final marking will be the load rating of the gate when opened while under load. This rating is also significantly less than the major axis load rating. Accidental gate openings are the number one reason for a carabiners failure.

Tri-Axle Loading

There will be no markings for a tri axle load strength rating. Tri axle load ratings will be similar to the strength ratings of a “cross loaded” rating. Tri axle loading occurs when three separate loads are placed in the carabiner and each load pulls from a separate direction.  This factor is possible to experience with any style carabiner but it is more commonly seen with the larger locking carabiners.

Differences in Carabiners

There is a wide variety of non-locking carabiners, including: Ovals, “D’s”, Light “D’s”, Off Set “D’s”, Bent Gate Off Set “D’s”, and a half dozen different wire gate designs.  Then, there is a wide barrage of locking carabiners.  The locking carabiners include: “D’s”, Off Set “D’s”, Pear Shaped, Mini Pears, Large Locking “D’s”, Bent Spines, Off Set Swing Gates. For each of these types of locking carabiners, there is a type of barrel on the gate of the carabiner to lock the carabiner into place.  These include Auto Lockers, Ball Lockers, and Screw Gate Lockers. Now take all of these carabiners and add in either a Tooth Lock or Key Lock gate design.  All of these diverse design variables create almost 100 different options to choose from when selecting the proper carabiner. If the wrong carabiner for the job is chosen less can be expected of the overall design of the system.

At a glance it appears there is no real reason to have this many variations of the same simple design.  It could even be argued that the selection is due to companies competing with each other for business. But think of all the shapes and designs for carabiners like this: at a tool store you can buy a 24 pack of screwdrivers with two different type tips, a Phillips tip and a Flat tip. Why would you need 24 different screw drivers?  The reasoning for this wide range of shapes and designs is apparent to anyone who has loosened or tightened those hard to reach screws. Each different screwdriver works at a different length, for a different screw.  Shape design for the carabiner is exactly the same and there is still room for improvement. Look at your carabiners as “tools” in the tool box for when you need them. Unlike a screwdriver that will only give you a cramp or a split knuckle for picking the wrong design, picking the wrong carabiner could, in certain situations, be a contributing factor to injury or death!

Let’s have a look at some of the differences of modern carabiners.

Non-Lockers

A non-locking carabiner is designed for many things, such as utility work, some static loads, organizing gear, used in a system with webbing to create lead climbing protection systems such as “quick draws”, etc...

Pros: lighter, faster to connect to in lead climbing scenarios.

Cons: can easily become disconnected from your system under dynamic movement and are significantly weaker due to the accidental or incidental opening of the gate even with the slightest bit.

Flushed nose oval (Old School)

Flush nose “D” (Old School)

Oval

When loaded properly material is centered between the gate and the spine transferring an equal amount of energy along either side of the biner. Typically, this weaker by design since all the strength of a carabiner rests in its spine.

“D”

When properly loaded material is sent into the “crotch or heel” transferring the majority of the energy into the spine of the carabiner making it safer to open the gate of the carabiner under minor loads. Typically a stronger carabiner by design.  

Bent Gate

My least favorite design but very popular amongst the sport climbing community. The bent gate allows a lead climber to load a rope into the carabiner a bit easier as the bent gate creates a cradle affect that compliments the rope into position. Similar to the off set “D”, the nonparallel design between the spine and the gate also make it harder to cross load.

Wire Gate

An ingenious design. Take a look at the strength ratings between a regular off set “D” and a wire gate off set “D” carabineer. The wire gate will be similar in strength along the major axis, and stronger in a cross load! There is twice as much material that will need to shear before the gate releases. Plus, the stainless steel gate design gives it a higher flex rating making it harder to open under sudden tension or shock load. For a test, take your regular gate carabiner and whack it against the palm of your hand and you will hear the sound of the gate opening, and then closing. Now take your wire gate and do the same. No sound! During a fall everything is in motion, and this is the one moment you need your system to be at its finest. As everything is pulling tight, one of your carabiners smacks against the rock and the gate opens slightly for a split second, dropping the strength rating of 22 kN down to 7 kN. This amount of force is very easy to generate on a short, hard fall. While soloing a route called “Swoop Gimp” in Zion, I fell out of my portaledge when it shifted from my movement. My primary attachment point was to a non-locking off set “D” by a standard daisy chain. I hit into my harness so hard the gate of the carabiner popped open and the nose bent completely out of the gates range, nearly failing the carabiner.

A wire gate carabiner will not open nearly as easy and is stronger if cross loaded.

Key Lock on the Left versus Tooth Lock on the Right

Tooth Lock

Now what about the tooth design? Basically this is a “Murphy’s law” situation where you can again slightly stack the odds more your favor. The tooth lock is great for situations where under no circumstances do you want to come out of your gear. As a last line of defense the tooth may get snagged in your gear (i.e. ascender, bolt hanger, belay loop, ect.). This idea is quite un-nerving and by no means a reason to lack redundancy in your system design, but none the less a thin layer of insulation against a complete release. Good to use for most climbing scenarios.

Key Lock

Great for situations where you may need to “escape the system”. By design a key lock is less likely to get snagged on rope or webbing under minor loads or dynamic movement. Perfect for situations where clipped in for protection from one element, while maintaining the ability to escape the system is equally important (i.e. most canyoneering scenarios, such as swimming while trailing a pull rope or tag line where a drowning scenario may exist, etc.).

Oval Locking Carabiners

Carry the exact same advantages and disadvantages as the non locking oval. Though some will swear by their use they are not good for much other than basic utility work as the screw devices will interfere with one another if used in an opposing gate situation for top rope climbing. The strength ratings are also compromised by an ovals ability to center the material between the spine and the gate. The additional thickness of the screw gate makes the overall opening clearance less than a regular oval.

“D” Shaped Locking Carabiners

Carry the exact same advantages and disadvantages as the non locking “D” carabiners. The locking D is better for utility work and is significantly stronger than the oval locker but is still far from a first choice design for most applications. The additional thickness of the screw gate makes the overall opening clearance less than a regular “D” shaped non-locker.

Off set locking “D” Carabiners

This design is by far the weapon of choice for any type of utility work. Ascending, most personal rigging to anchor points, and the “West Coast Canyoneering” style is dependant upon the off set locking key lock at the end of the chain reactor.

Belay/Mini Pear Biner

This carabiner is designed to be used for rappelling, belaying or rigging where “tri axle” loading is not a concern. This design is a bit weaker as the top heel/nose area is longer making it easier to leverage the nose lock out of the gate area.

Large Pear Shaped Locking Carabiner

In Rock Climbing, this is perfect for rigging master and hot points on top rope anchors. In Canyoneering, large locking pears can be used as carabiner blocks for static anchors. These can also be used for rappelling with larger diameter ropes, general rigging scenarios, etc. “Tri-axle” loading will significantly weaken the carabiner.

Auto Locking Carabiner

Pros- Auto locking carabiners take away the chance of forgetting to not lock a carabiner, or for time when a panicked person may try to open the carabiner, (i.e. zip lines or rescue).

However, we own over 400 carabiners and only 3 are auto locking! 

Cons- Gate mechanisms jam quite easily when dropped in sand or dirt. When wet under freezing conditions the mechanism will freeze shut. Should never be used when Canyoneering! On a wet and sandy rappel your rappel device will wring sandy water out of the rope that will build up inside the carabiners auto locking mechanism leaving you trapped with a carabiner that will possibly not open.  This becomes a huge problem when you bring in a pool of water adding to the possibility of hypothermia, drowning, etc...

Why are some carabiners colored and others not?

Carabiners shed aluminum oxide that discolors equipment, hands, clothes, etc. The colored anodizing factors help to significantly reduce the discoloring.  Also helps to keep the stinging down on cut up hands during multi-day climbs.

The Bottom Line

A carabiner is designed for linking aspects of material (hardware, ropes, slings, etc.) together to create systems that will protect and save lives. Carabiners are strong when used in the right situation. However, when misused, carabiners can be incredibly weak! Because of the dynamic nature of vertical risk adventure sports, redundancy (when possible) is a key to success. Systems that lack redundancy are viewed as less dynamic and greater care should be taken during the design and execution of skill sets applied to these systems.