Surpassing chalk, puffy jackets, and beer (OK, and ropes too), carabiners are the most essential piece of the climbing life. These small metal clippers are both the staple of any rack and the icon by which non-climbers identify our sport. Once a simple concept—a metal oval with a spring-loaded gate—the intended uses, designs, and details of the carabiner have grown exponentially from their original purpose: helping soldiers carry their inventory efficiently. Below, we outline the history of the carabiner, important vocabulary, and the rest of the basics of these clippers’ designs so you can pick the best biner for the job.

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Building the Biner

All carabiners begin their lives as a tube of extruded aluminum alloy called rod stock. The alloy consists of aluminum, which is naturally lightweight and pliable for easy forming, and zinc, which adds strength. This combination maintains full strength with a scant weight. A machine bends the stock into a rough oval shape that will concentrate the force onto the straight spine, then a forging machine presses this shape between two dies (similar to a mold) which apply great pressure to form the final template of the carabiner. A trim press then cuts away the excess metal. Thousands of gateless, rough, gray biners are then heated again to strengthen the alloy in its new shape. Once cooled in water, the biners move through vibrating drums and tumble with wet stones to remove any unwanted texture or rough edges that would damage ropes and webbing. After being polished in another drum, some of the biners get painted, and workers put gates on by hand. Finally, every carabiner is tested for gate function. A machine pulls along the length of the carabiner, simulating the load of a 200 lb. climber, while simultaneously opening and closing the gate to ensure the biner does not fail. Quality control selects samples from each batch for more rigorous testing, and the remaining carabiners are stamped with codes, certifications, and brand logos.

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Sample Testing

The quality control lab is basically a carabiner torture chamber, full of devices and machines designed to test biners in many load and stress scenarios. Tensile testers slowly pull the carabiners until they fail: Carabiners must withstand a minimum of 20kN (4,900 lbs.) along the major axis (gate closed), and 7kN (1,500 lbs.) both along the minor axis and along the major axis with the gate open. Unique drop-tower setups test other scenarios, like if a biner is loaded over a rock edge, how a worn biner surface interacts with the rope, or how back-clipped biners perform during a fall. Variables can be adjusted to simulate dynamic and static belays, and cycle devices test gate function after 10,000+ gate openings and closings. While those base-level strength ratings are more than enough for standard climbing uses, companies use benchmark manufacturing statistics to ensure that more than 99% of the carabiners produced are actually stronger than those numbers in real-world scenarios.

Shape up

There are a handful of carabiner shapes, and each has advantages and disadvantages. The most common is the D-shape with a completely straight spine and a sharp bend at both ends, which cuts down on weight but increases strength. The oval is symmetrical and more of an old-school shape. These are typically cheaper and very durable, but slightly weaker (still fully certified) and heavier. Pear-shaped carabiners have a spine that bends outward, away from the spine, to form an even bigger and more curved rope basket. These are great as belay biners, especially if belaying with a Munter hitch or tube-style belay device, because the sizable basket prevents twists and kinks in the rope. They are larger and therefore heavier, so they’re best saved for a single belay or anchor biner.

Carabiner Vocab

Gate (1):The spring-loaded pivoting piece opposite the spine. The gate swings shut to close against the nose.

Standard – This gate is a solid tube shape (pictured), making it slightly heavier with more gate flutter due to increased mass.

Wire – This is typically a U-shape that hooks onto the nose. And while it has a lighter weight, it’s slightly less durable.

Straight vs. Bent – Used to describe both standard and wire, a straight gate runs in a continuous, straight line, while a bent gate has a slight angle in it. The former is usually reserved for clipping to a bolt or a piece of gear, while bent biners receive a rope more smoothly.

Double – This is a more recent innovation (also called twin gate), with two sets of rivets and two gates that open opposite each other, acting as a sort of locking mechanism.

Spine (2):This is the long section of the carabiner opposite the gate that usually has the strength ratings, certifications, and brand stamped on it. When a biner is under weight, most of the force is directed to the spine, which is the strongest individual section of the biner.

Rope Basket (3): The large bend at the top of the spine that the rope runs through. This open curve minimizes wear on the rope and the biner.

Runner End (4):This is the smaller bend opposite the rope basket where a runner would sit, but the rope, belay device, and other gear can also occupy this space.

Nose (5):At the top of the opening for the gate, this is where the gate is latched while closed. Some are notched to accept wire gates, but the keylock style is smooth, which prevents the biners from snagging on bolts and gear when cleaning.

Locking: A mechanism on the gate prevents the biner from accidentally opening; it’s required in certain situations, such as belaying and clipping in direct to the anchor. There are several types, listed below.

Screw – The gate is threaded and a metal cylinder must be manually spun up to cover the nose, which locks it closed.

Twist – The gate is sheathed in a spring-loaded cylinder that will only open when twisted into a certain position. These automatically lock when the gate shuts.

Magnetic – Magnets on either side of the nose keep metal prongs against the nose, which mechanically prevent the gate from opening. Pinch the sides of the gate to lift the prongs away from the nose and open it.

Understand the Standards

A kiloNewton is the unit used to measure carabiner strength, and it can be tricky to understand in climbing scenarios because it’s not a static force. Instead, it means mass times acceleration, or how much weight is moving times the accelerating force of gravity. For a better real-world understanding of this measurement, you can think of 1kN as approximately 225 pounds. The major axis is the long side of the carabiner, which runs parallel to the spine, while the minor axis is perpendicular to that. The strongest orientation is always along the major axis with the gate closed. Applying force on the minor axis is called cross-loading, a dangerous situation since this axis is much weaker. Modern climbing biners are rated to at least 20kN along the major axis with the gate closed, and 7kN along the minor axis and with the gate open. But how did companies arrive at these numbers for industry standards? The German military found that parachuters jumping out of planes could withstand up to 12kN in a full-body harness, so this became a standard for harnesses and ropes. When determining how strong a biner needed to be, engineers took into account the force from the rope on the biner and found that the belay side had to hold 8kN. This breaks down to 12kN on the climber’s side and 8kN on the belay side, so 20kN total. The 7kN rating was determined after a series of field accidents where carabiners were failing at a rating of 6kN, so the regulation was upped to 7kN.

History of the Carabiner

By Jordan Achs