page_title: Hex key
section_title: Variants
hierarchical_section_title: Hex key / Hex key standard sizes / Variants
caption_attribution_description: English: Allen Wrech with ball end Español: Llave Allen con punta de bola
context_page_description: A hex key, Allen wrench or Allen key, is a simple tool used to drive bolts and screws with hexagonal sockets in their heads.
  The tool is usually formed of a single piece of hexagonal rod of hard steel, with blunt ends that are meant to fit snugly into the screw's socket, bent in an "L" shape with unequal arms. The tool is usually held and twisted by the long arm, creating a large torque at the tip of the short arm. Reversing the tool lets the long arm reach screws in hard-to-reach places.
  Each key is meant to be used with screws of a specific socket size, with rather tight tolerances; so the tool is commonly sold in kits that include half a dozen or more keys of different sizes. Usually the length of the key increases with the size of the socket, but not necessarily in direct proportion.
  Variants of the tool have the short end inserted in a transverse handle, which may contain multiple keys that can be folded into the handle when not in use.
  The "Allen" name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut circa 1910, and currently owned by Apex Tool Group, LLC.
context_section_description: A security version of the hex head includes a pin in the center. These fasteners are said to have a "center pin reject" feature to prevent standard hex wrenches from working. A special driver must be used to fasten or remove these fasteners. The TORX head's security variant also has such a pin for the same reason.
  Some hex keys have a ball on one end, which allows the tool to be used at an angle off-axis to the screw. This type of hex key was invented in 1964 by the Bondhus Corporation, and is now manufactured by several other companies. While providing access to otherwise inaccessible fasteners, thinning of the tool shaft to create the ball shape renders it weaker than the straight-shaft version, limiting the torque that can be applied. The tool also makes point contact with the fastener as opposed to the line contact seen in the straight style tools.
caption: Hex keys of various sizes with ball ends.
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