Key (Tool)

Key . (From the Latin clavis ). Type of tools used to tighten or loosen elements that are joined by screws or nuts. They are usually entirely manual, but there are variants added to pneumatic devices or portable motorized pistols.


The keys are made of an alloy of steel with  chromium  and  vanadium . They come in sets that typically range from a 6-millimeter to 24-millimeter muzzle, except for Allen keys, which may have smaller dimensions.

Three parts can be identified in the structure of almost all the keys: the head is the end that contains the mouth , and the body is the central bar, usually with an H profile to give it resistance.

Types of keys

By mouth . They usually have sockets on both ends, calibrated for nuts of different sizes.

By eye . Its mouth is internal in the form of an eye or a ring, which allows it to achieve a greater grip than ordinary open-end wrenches.

Extension . Also called adjustable mouth . One of the legs has a sliding mechanism that can be adjusted to a suitable distance by means of a screw, for which reason the same key is used for the different calibers.

Of cube . Its main element is a cube-shaped mouth in which the nut is housed. It has the advantage that it produces a great grip, without the possibility of skating. The hubs generally come separately, in sets, and are inserted into a properly designed arm. The arm may have a ratchet mechanism so that it is not necessary to remove the hub from the nut as it is tightened (or loosened), which saves a lot of time and effort.

Pressure . They have a mechanism to firmly fix the jaws and prevent slipping during high pressure work.

Allen . They commonly have an L-shaped arrangement, and each end is calibrated with different measurements. They are used for screws that have a hexagonal hole in the head, unlike normal screws that have that shape on the outside of the head. A variant is the pipe wrench , specially designed to open the caps of the fuel pipes (tanks) .

For tubes . One of the variants consists of a chain of plates that can be fixed in various openings to clamp tubes of different dimensions. The so-called Monkey Wrench or Stillson Wrench has a fixed or adjustable part with the same purpose. (See corresponding pages).

Two-handed . The arm has a T-shape to be operated with both hands and thus achieve a high torque. The most typical of this model is the one used to loosen or tighten the bolts (in Cuba called cranes ) of the wheels of vehicles.

Eight mouths . It is a wrench specially designed for cyclists, which has eight eye sockets with different gauges for a wide range of nuts.

Ratchet . Its mouth ends in a shoulder that is inserted into the carved notches in a specially designed nut .

Dynamometric . It is a variant of the ratchet for the socket wrenches, being equipped with a mechanism that indicates when the appropriate tightening tension level is reached, achieving high precision.

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