Not many other pieces of hardware are so crucial for climbing like the carabiner. No matter if you tie into your harness, build an anchor or connect safety devices for belaying or rappelling – carabiners are use everywhere. They are the one piece of metal in climbing, used to connect ropes and slings, ropes with other ropes – basically everywhere where you want a quick method of connection or moving rope is involved. But what does it mean to cross load a carabiner? Short answer: Every carabiner has a main load direction. To cross load a carabiner means to put a force on it that is rotated 90 degree from the main loading direction. The carabiner is usually much weaker in this other direction. It breaks easier in this direction. I’ll also show you what to avoid, and give some more tips regarding hardware safety.
Most modern carabiners are so easy to use that it’s almost impossible to mess it up if you have basic training. But keep in mind, margins for error are little if you screw up. A  failing carabiner means a potentially fatal problem. One thing you must avoid at all costs is cross loading.

How a rock climbing carabiner works

Engineers design rock climbing carabiner to take loads along one certain axis. This axis is very near to the Arrow pointing up and down in the figure below. We call this line “spine” of the carabiner. This is the direction where the carabiner can withstand the strongest force. If you load it in any other direction, it will be weaker.
You will find how strong it is in this main direction as a marking on the carabiner. The marking includes an arrow that points in the direction of this spinal loading direction. The unit used for these markings is kilo-Newton which equals thousands of Newtons, abbreviated kN. 1 kN equals roughly 225 pounds of force.
To give you an example: 1 Newton equals the force you need to accelerate a block of steel of 1 kg at a rate of 1 meter per second squared. If you accelerate a person of 100 kg at a rate of 10 meter per second squared, it gives 1 kN. 10 meter per second squared is roughly the acceleration on earth when you hang something to the carabiner dangling in the air.
Theoretically, you could use a carabiner that is rated to 22 kN to hold a weight of around 2000 kg – or 2 metric tons. Sounds a lot right? But, keep in mind, if this weight falls free for some time, the forces are much higher, so this is just a theoretical value.

What it means to cross load a carabiner – detailed explanation

Now lets discuss a cross load. The middle picture shows a cross load. Any force in this direction is marked on the carabiner with a left right arrow. A carabiner can usually  take a considerably smaller load in this rotated direction than in the main loading direction. It comes down to the   design of the carabiner: In this direction, there is less material to support the load.

The gate of the carabiner takes some load too, even if you load the carabiner in the main direction. And that’s why you will find another symbol on the carabiner for this. It indicates the possible load when the gate is open. It’s usually much less than with a closed gate, as an open gate cannot load force.

The gate is also part of the reason why the maximum loading force for a a crossload is so low. For the case that the force pulls inwards, the gate is only held in place by the locking sleeve and nothing else. And as a carabiner is only as strong as it’s weakest part, it means you have a low strength when load goes in this direction. It’s higher when you load outwards, as the locking sleeve and the gate itself pushes against the rest of the carabiner in this case.

What does it mean to cross load a carabiner

Three types of carabiner loading: Correct, Crossloading and Tri-Axis loading

Other bad loading scenarios: Tri-Axial loading and nose-hooked carabiners

Another weak point of a carabiner is when you load in directions completely away from the spine. You can find this scenario in the right picture. It’s described in more depth here. The load a carabiner takes in this direction can be even weaker than a cross load. The same applies to the so called nose-hooked carabiner.

What’s a nose-hoked carabiner?

What does it mean to cross load a carabiner

Nose-hooked carabiner – Source: Black Diamond

A nose-hooked carabiner happens when your contact point squeezes open the gate at the nose of the carabiner. It’s a really bad situation, which can result inf carabiners failing at less then 10% of their rated closed gate strength. For our example this is around 227 kg of a load hanging in free air. Source here. This amount of force can happen if you have even just a small fall or bounce test

Why is a nose-hooked carabiner so bad?

Why is the carabiner’s breaking strength all of a sudden so low when nose-hooking it? It’s because this scenario combines an open gate with the design of the carabiner and a weird position for the force to attack. By putting load on it now, you basically create a cantilever that pulls the carabiner basket off of the bolt hanger.

As the load is not in line with the spine axis, which is the main direction to load the carabiner, the carabiner becomes excessively twisted and torque builds up in the material. It then breaks at the weakest point, which is the upper part like shown in the picture.

What does it mean to cross load a carabiner

Broken carabiner due to nose-hooking. Source: Black Diamond.

 

Tips to use a carabiner safely to avoid cross-loading and other dangerous loads

If you want to be safe, you must avoid the scenarios from above. Focus on two things:

1 . Always ensure that the carabiner has a closed gate when it is loaded

If you have a screwing lock sleeve, make sure to screw it closed when you place the carabiner. Make also sure that you have no rope etc. wound up around the screw – it could accidentally open the carabiner. If you use a screw-lock carabiner on your belaying device, make sure to turn the screw lock side away from moving parts – aka your hands handing in or out the rope. For non-screw carabiners, place the carabiner in a way that loads are not opening the gate.

2. Place the carabiner correctly in the direction of the load

This makes sure to avoid loading it from more than one direction. Never load the carabiner in opposite directions, try to avoid tri axis loading as much as possible. If you build equalized anchors, try to move the anchors as close together as possible to minimize off-axis loading

3. Never place a loaded carabiner on an edge or ledge

Placing a carabiner on  a ledge will basically break the carabiner with the force of the ledge pushing against it, creating lots of torque and twist.

4. Avoid bulky knots around the carabiner

Bulky knots can lead to off-axis loading too, if you want to know more about it read here.

Conclusion

If you liked this article, make sure to read my other articles about top rope anchors, how to built perfect anchors, the best climbing shoes of 2020, and why should always wear a helmet when rock climbing. Feel free to leave me a comment too, if you have suggestions and ideas.