An Allen key is an L- or T-shaped tool with a hexagonal cross-section, used to tighten or loosen bolts and screws that have an internal hex socket. Such a bolt is also known as a hex socket bolt.
Origin and use
- The name “Inbus,” used in Dutch and German, comes from the brand and abbreviation INBUS, standing for the internal-hex screw of Bauer und Schaurte.
- In English this tool is called an “Allen key” or “Allen wrench.”
- Widely used for tasks such as furniture assembly and machine building, where compact, recessed fastenings are practical.
Sizes and variants
- Sizes in millimetres: the size refers to the width across the flat sides. Common sizes range from 2 to 10 mm.
- Ball-point: some versions have a ball-shaped tip so you can turn the bolt at an angle as well, handy in hard-to-reach places.
Because of the hexagonal connection, an Allen key transfers force onto several faces at once, giving a good grip when tightening and loosening.
Related terms
- Wedge anchor bolt
- Folding rule
- Spirit level
- Builders’ hardware
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