A carabiner (/kærəˈbiːnər/) or karabiner is a metal loop with a spring-loaded gate[1] used to quickly and reversibly connect components in safety-critical systems. The word is a shortened form of Karabinerhaken, German for ‘spring hook for a carbine’. Carabiners are widely used in rope-intensive activities such as climbing, arboriculture, caving, sailing, rope rescue, construction, industrial rope work, and window cleaning. They are made from both steel and aluminium. Those used in sports tend to be of a lighter weight than those used in commercial applications and rope rescue. Carabiner-style keyrings have also become popular, most stamped with a “Not For Climbing” warning. Use Carabiners are widely used in rope-intensive activities such as climbing, arboriculture, caving, sailing, rope rescue, construction, industrial rope work, and window cleaning. They are made from both steel and aluminium. Those used in sports tend to be of a lighter weight than those used in commercial applications and rope rescue. Carabiner-style keyrings have also become popular, most stamped with a “Not For Climbing” warning. Physical properties Shape Carabiners come in four characteristic shapes: Oval: Symmetric. Most basic and utilitarian. Smooth regular curves are gentle on equipment and allow easy repositioning of loads. Their greatest disadvantage is that a load is shared equally on both the strong solid spine and the weaker gated axis. D: Asymmetric shape transfers the majority of their load onto the spine, the carabiner’s strongest axis. Offset-D: Variant of a D with a greater asymmetry, allowing for a wider gate opening. Pear/HMS: Specialized oversized offset-D’s used in belaying. These are usually the heaviest carabiners. Locking mechanisms There are three broad categories of carabiner: auto locking, manual locking, and non-locking. Non-locking Non-locking carabiners have a sprung swinging gate that accepts a rope, webbing sling, or other hardware. Rock climbers frequently connect two non-locking carabiners with a short length of nylon web to create a quickdraw. Three gate types are common: Straight gate: The most utilitarian, and hence most popular. Bent gate: Curved gates allow for easier clipping in and out in special situations, such as connecting a rope to a quickdraw. Gate strength remains on a par with straight-gate carabiners. Wire gate: The lightest type, with a strength roughly equal to the others, allowing more to be carried for a given weight. Wire gates are less prone to icing up than solid gates, an advantage in Alpine mountaineering and ice climbing. The reduced gate mass makes their wire bales less prone to ‘gate flutter,’ a dangerous condition created by irregular impact forces generated by the climbing rope or contact with hard surfaces in a fall which momentarily opens the gate (and both lowers the breaking strength of the carabiner when open and potentially allows the rope to escape). Locking Locking carabiners have the same general shape as non-locking carabiners but have an additional mechanism securing the gate. These mechanisms may be either threaded sleeves (“screw-lock”), spring-loaded sleeves (“twist-lock”) or magnetic levers (“Magnetron”). Screw-lock: Have a threaded sleeve over the gate which must be engaged and disengaged manually. They have fewer moving parts than spring-loaded mechanisms, are less prone to malfunctioning due to contamination or component fatigue, easier to employ one-handed. They, however, require more total effort and are more time-consuming than twist-lock. Twist-lock: Have a security sleeve which must be manually rotated to disengage, but which springs closed automatically upon release. They offer the advantage of re-engaging without additional user input, but being spring-loaded are prone to both spring fatigue and their more complex mechanisms becoming balky from dirt, ice, or other contamination. They are also difficult to engage one-handed and with gloves on. Magnetic: Have two small levers with embedded magnets on either side of the locking gate which must be pushed or pinched simultaneously to disengage. Upon release the levers pull shut and into the locked position against a small steel insert in the carabiner nose. With the gate open the magnets in the two levers repel each other so they do not lock or stick together, which might prevent the gate from closing properly. Advantages are very easy one-handed operation, re-engaging without additional user input and few mechanical parts that can fail.