Carabiner Terminology and Design

Strengths: Carabiners are given three strength ratings - the first is the strength along the length of the carabiner with the gate closed (20kN+), the second is the strength across the width of the carabiner (7kN+) and the third is the strength along the carabiner with the gate open (7kN+). It is important to realise from these ratings that the carabiner is much weaker if the gate is open or the load is applied across its width (cross-loading). Climbers usually take great interest in the open-gate and cross-loading strengths for this reason, but a more important consideration is ensuring these scenarios do not occur in the first place with good carabiner design, such as stong gate springs.

Strengths are given in kiloNewtons (kN), a unit of force. 20kN roughly translates as a 2,000kg mass hanging from the carabiner. Although a climber may weigh only 80kg he will generate a much stronger force when falling.

Non-locking, Locking, Autolocking: Most climbers prefer to use a locking carabiner for constructing anchors, tying into ropes and clipping a belay device to their harness. The manually operated lock prevents the gate opening accidentally.

An autolocking carabiner automatically locks when the gate is closed. They are quicker and easier to unlock - perhaps too easy which is why non-auto locking carabiners are used by most. Autolocks are good for instruction and beginners who may forget to lock the carabiner.

Non-locking carabiners are used for all situations when speed is necessary including racking gear and placing protection. They are also considerably lighter.

Gates: Non-locking carabiners have either solid or wire gates. Solid gates can be either straight or bent. A quickdraw comprises one straight and one bent gate - the straight gate clips the bolt or protection and the bent gate clips the rope.

Although solid gates are still widely used, they are outperformed by wiregates in every respect. Wiregates are lighter, open wider, won't freeze shut and are easier to grip. The major advantage of wiregates is their low gate flutter - the most important consideration when choosing non-locking carabiners. If the lead climber takes a large fall the gate of the carabiner holding the rope at the last piece of protection can be shaken open by the rope. This is simulated by hitting the spine of a carabiner against your palm and listening for the gate opening and closing. For a wiregate this is barely noticable. Studies have shown that as a solid gate is only 1/3 through opening a wiregate has already closed.

Steel vs Alloy: Climbers use aluminium alloy carabiners because they are light. Care should be taken with alloy carabiners because if they impact on a hard surface invisible cracks will form, weakening the carabiner. Simply, if you drop a carabiner onto rock you must retire the carabiner. Steel carabiners are therefore safer and used in commercial operations and climbing gyms where they get daily use but don't have to be carried far.

Wide Aperture (Great Capacity): The aperture of a carbiner is how wide the gate will open - allowing protection, slings and ropes to be clipped. In most cases the aperture only needs to be wide enough for a rope to be clipped, yet the carabiner on the harness belay loop should be large aperture as it needs to hold the belay loop, belay device and potentially two ropes.

Ovals: Oval carabiners aren't quite as strong as the "D" shaped carabiners, but they have specialised uses. For climbing they are useful for racking protection (a lot of wires can fit on one oval) and aid climbing (beyond the scope of this discussion).