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Carabiner: A Climber's Best Friend

Carabiner History

Carabiners are widely used in tree climbing for so many different tasks it's unbelievable. From rigging setups, to mechanical advantage to the basis of your climbing system, these little metal ovals really make our lives easier when up in the tree. Though they are a climber's best friend, carabiners have been around for way longer than you may probably think as well, and weren't initially used for climbing purposes. So let's look at the history of the carabiner and review their various shapes and uses over the years.

Carabiners were originally used on Carbine rifles to attach the carrying strap by a metal hook with a spring locking gate. This helped soldiers carry their rifles long distances and easily unhook the strap when needed. Surprisingly, some of these designs date all the way back to 1868! That means some form of carabiner has been around for almost 150 years!

German rock climber, Otto Herzog, started experimenting with steel carabiners for rock climbing in 1911 after using fireman's tools at work. Herzog developed a steel biner with a spring loaded opening; however, the gate was fairly unreliable. This led to further development in the European rock climbing community and eventually helped Alpininst Pierre Allain to create a D shaped carabiner that shifted the strength to the spine of the carabiner. This resulted in a much stronger design, as well as a nose that was less prone to snagging.

Since then, carabiner design has continued to advance in terms of both style constructions and different locking mechanisms. All of these later developments have created a safer design for rock climbers and tree climbers alike. Whether it be the brilliant ball lock design that Petzl uses or the beautifully machined Ultra Os from DMM, carabiners are now a mainstay in a climber's gear bag.

Carabiner Construction

Carabiners are made up of several different parts that allow them to work as well as they do. Here is the basic break down of carabiner construction:


The gate is a spring loaded opening that is capable of closing or locking with various locking mechanisms styles. Any carabiner used in the arboricultural industry for life support should be double locking, which means that two deliberate actions must be made before pulling open the gate. This reduces the chances of a gate unintentionally opening while aloft.


The nose of the carabiner gives the design strength as well as keeps gear from slipping off the carabiner until needed. The nose usually locks into the gate with a keyhole shaped slot. When the carabiner is loaded, the nose locks into the gate and creates a complete circle to provide more strength.


The spine is the backside and back bone of the carabiner, as it provides the carabiner's strength. Gear is usually pushed towards the spine to put the load on the strongest part of the device. Carabiners used to simply be made of extruded straight stock, but many are now being made with I-beam construction, making for even stronger and more reliable gear!


The baskets are where gear is held inside the carabiner. There is a basket at the top and one at the bottom. The different shapes of carabiners usually lend themselves to different shapes within the baskets. This was originally developed for different belaying techniques while rock climbing. Now it helps when using different systems such as a Rope Wrench setup, where more room is needed in the basket for your prussic, Rope Wrench tether, and Hitchclimber pulley.

Carabiner Styles

Carabiners come in a variety of different shapes and sizes and each one has a different use. Let's take a look at some different shapes that are typically used in tree work and see what makes each one unique!

D Shaped

D shaped carabiners allow rope and webbing to slide to the back towards the spine to create a stronger construction.

Oval Shaped

Ovals are an old school design that has held up to the test of time. The oval pushes gear towards the absolute bottom and the absolute top of the carabiner for a symmetrical load.

Pear Shaped

A Pear shaped carabiner has an outwardly bent spine that creates a larger basket. This allows a climber to put even more gear on the device.

Determining Device Rating

Carabiners have markings on the side of the spine that tell you how much each part of the carabiner is rated for. Each set of arrows has a small diagram next to it differentiating between the different parts.

Arrows pointing towards each end of the carabiner define how much force it would take to break the carabiner along the spine (usually the highest rating). Arrows pointing out at each side of the carabiner, one towards the gate and one towards the spine, define how much force it would take to pull the carabiner apart in that direction (usually much less).

A diagram with the gate of the carabiner open provides the force needed to pull the carabiner apart if the gate were to be open (usually the lowest).

You will also see a number with the letters kN next to it. This is the marking for a Kilonewton. A Kilonewton is a measurement of force that can be roughly equated to 225 lbs. So with some simple math you can multiply the number on the carabiner by 225 and get the breaking strength of that section of the carabiner.

Carabiners for life support must be rated to at least 22.5 kN or 5,000 lbs according to ANSI. Keep this in mind when buying from companies that sell gear other than Arborist gear. Always check the markings to make sure you are using a carabiner that is rated for life support!

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