Vertical caving terminology and methods > General hardware
Similar to a carabiner, but the gate is not hinged. Instead, it is screw threaded so you screw it slowly across the gap. Much stronger. Much smaller. Much lighter weight. Much slower and more annoying to use. Generally used for rigging. Often used for a D-ring. Some are delta/triangular, to allow three directional attachments, or to allow flat straps like slings to lie along one of the edges. Some twist 90° along the length of the maillon, in order to rotate the equipment they are attached to, which can also be used to push a rope further from the rock, to avoid rope rubs created by some types of hangers. The ratings of maillons vary widely depending on whether they are made of aluminium or steel, and how big they are. If they are going to be used for life critical purposes, such as for rigging, they should be PPE rated (European standard EN 12275), with a minimum breaking strength (MBS) at or above 2.5 tonnes (actually given as a breaking strain of 25 kN), but especially strong versions may be rated as high as 22.5 tonnes, just in case you ever needed to play tug-of-war with a Chinook helicopter.
When used in reality on a hanger, a maillon with a stated MBS of 2750 kg, that would otherwise have broken at 3574 kg in a very careful test with a wide radius, would break at 2632 kg when pulled against a hanger; the hanger takes a tonne off the strength, compared with a wider radius. However, maillons can become damaged from heavy use, and at that point, the strength can no longer be assumed. Once damaged by rubbing against other equipment like hangers, so that a significant portion of the maillon's material is missing at one end, the strength loss is very complex. The notch concentrates the force, and sharper edges of the notch will increase this further. The specific type of metal will play a part. The strength of the maillon comes largely from its shape, with less strength coming from the material thickness, and so in actual testing, the strength loss was surprisingly little. However, there will be a point at which the strength loss dramatically increases, and catastrophic failure can happen quite suddenly. Corrosion has a similarly complex effect, depending on which part it has compromised, particularly if the screw threads are affected, and how far through the material the corrosion has advanced. As a result, damaged maillons should be replaced before the damage becomes significant, not assuming that it is possible to estimate how much strength remains.
French blacksmith Firmin Desbiolles invented and made the first maillons in 1923, for the purpose of linking chains for farming. He applied for the patent in 1941. Around 1945, he assigned the patent to Francis Péguet, whose family business Péguet has made them ever since.
This history section only covers maillons. This article also has a detailed history of many of the other devices and techniques that are used for vertical caving.
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