A hex key (also known as a hex wrench, Allen key, Allen wrench, or Inbus) is a simple tool for driving bolts or screws with internal hexagonal recesses (sockets).
Hex keys are made from a single piece of strong hexagonal steel rod with blunt ends that fit neatly into similarly shaped screw sockets. Bending the rods to 90º results in two arms of uneven length, resembling a “L”.
The tool is normally held and twisted by its long arm, providing a relatively considerable torque at the tip of the short arm. However, it can also be gripped by its short arm to access screws in difficult-to-reach spots and turn screws quickly at the sacrifice of torque.
Hex keys are labeled with a socket size and made to precise tolerances. As a result, they are frequently marketed as kits containing a variety of sizes. Key length often rises with size, although not necessarily in proportion. Variants of this design include the short end inserted in a transverse handle, which may hold numerous keys of varied sizes and folds into the handle when not in use.
While the “Allen” name is commonly used in generic terms for “hex key,” it is a registered trademark (about 1910) of the Allen Manufacturing Company (now Apex Tool Group) of Hartford, Connecticut; nonetheless, “Allen key” and “Allen wrench” are often considered generic trademarks.
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History Of Hex Key
The concept of a hex socket screw drive was most likely developed between the 1860s and the 1890s, although such screws were not manufactured until around 1910. According to Rybczynski (2000), from the 1860s to the 1890s, there was a surge in patents for alternate drive types in the United States.
which are proven to have internal-wrenching square and triangle types (that is, square and triangular sockets) (U.S. patent 161,390), but he explains that these were patented but not built due to the challenges and costs involved at the time.
P. L. Robertson of Milton, Ontario, commercialized the square socket in 1908 after perfecting and patenting a suitable cold forming procedure employing the appropriate material and die design. In 1909-1910, William G. Allen developed a process for cold-forming screw heads around a hexagonal die (U.S. patent 960,244).
Published ads for the “Allen safety set screw” by the Allen Manufacturing Company of Hartford, Connecticut, exist since 1910.
In his autobiography, the creator of the Standard Pressed Steel Company (SPS; now SPS Technologies, Inc.), Howard T. Hallowell Sr., gives a version of events
In 1911, SPS developed a hex socket drive in-house, independent of Allen. This resulted in the Unbrako product range. Hallowell’s story makes no mention of the Allen patent issued in 1910 or the Allen safety set screw product line. Hallowell does, however, explain the same inspiration indicated by Allen for a wave of hex socket head adoption, beginning with set screws and progressing to cap screws.
This was an industrial safety effort, part of the greater Progressive Movement, to install headless set screws on the pulleys and shafts of the line shafting, which was common in factories at the time. The headless set screws are less prone to catch workers’ clothing and bring them into contact with the running shaft, causing injury.
At the time, SPS was a well-known manufacturer of shaft hangers and collars, the latter of which were secured with set screws. In search of headless set screws with a superior drive than a straight slot, Hallowell stated that SPS had found square-socket drive set screws from Britain, but they were prohibitively expensive.
This cost issue motivated SPS to purchase its first screw machine and produce its screws in-house, leading in SPS’s entry into fastener sales (for which it later became well-known in the metalworking sectors).
Hallowell added, for a while, we experimented with a screw with a square hole like the British screw, but quickly learned that they would not be acceptable in this nation.We chose to include a hexagon socket into the screw.
Hallowell does not explain why SPS determined that the square hole “would not be acceptable in this country,” but it appears that it would have required licensing Robertson’s patent, which would have defeated SPS’s goal of lowering the cost of internal-wrenching screws (and could have been unavailable at any price, as explained at “List of screw drives > Robertson”).
The story of whether SPS’s procedures necessitated the license of Allen’s 1910 patent is not addressed in Hallowell’s memoir. The text does not say whether SPS used cold forming or linear broaching in its early years. If the latter was employed, Allen’s patent would have been irrelevant.
This acceptance began in tool and die work and spread to other production industries such as defense (aircraft, tanks, submarines), civilian aircraft, automobiles, bicycles, furniture, and others. Regarding the dissemination of the screws and wrenches, Hallowell stated that “the shift from a square head set screw Hallowell refers to the then-ubiquitous external-wrenching square drive to a hexagon socket head hollow set screw
The need to produce unique keys or wrenches for tightening or loosening the screw caused more swearing among mechanics and machine manufacturers than any other single event.
I am confident that those who read this book will have vivid memories of that time period. These transitional growth pains resemble those seen several decades later with the advent of the Torx drive.
World War II, with its extraordinary push for industrial production of all kinds, was most likely the first time most laypeople encountered the internal-wrenching hexagon drive. (In 1946, Popular Science magazine reported that “cap screws and setscrews with heads recessed to take hexagonal-bar wrenches are coming into increasing use.”
Features
Some features of hex keys include:
- The tool is basic, tiny, and lightweight.
- The screw or bolt’s contact surfaces are protected from external damage.
- There are six contact surfaces between the bolt and the driver.
- Small bolt heads can be accommodated.
- The tool supports the use of both headless and recessed-head screws.
- The key can hold the screw while it is placed into the hole.
- The torque imparted to the screw is limited by the length and thickness of the key.
- The tool is inexpensive to make, so it can be included with goods that need end-user assembly.
- Either end of the tool can be used to maximize reach or torque.
- The tool can be reconditioned by grinding the worn end.
Nomenclature
The term “hex key” is best known as “Allen” in English-speaking countries like the United Kingdom, Australia, Canada, and the United States, as well as in Spanish-speaking countries like Spain and Mexico.
Apex Tool Group, LLC presently owns the company, which was acquired by Bain Capital in 2014.
In Germany, the name “INBUS” is a registered trademark, initially an acronym for Innensechskantschraube Bauer und Schaurte, introduced in 1934 by the German business Bauer & Schaurte, and acquired in 2015 by INBUS IP GmbH, Breckerfeld, Germany.
INBUS IP GmbH was established with the claimed intention of owning and licensing the INBUS trademark. In late 2015 to early 2016, the business issued cease and desist orders to companies utilizing the name “Inbus” for hex keys.
HaFu Werkzeugfabrik H. J. Fuhrmann GmbH, Breckerfeld, North Rhine-Westphalia, currently manufactures INBUS products, accounting for 7% of the company’s EUR 8 million turnover in 2017.
In Scandinavia, it is known as the “Unbrako” key or wrench (originally founded in 1911 in Pennsylvania and bought by Deepak Fasteners Limited in 2008).
In Italy, it is known as brugola, after the business Officine Egidio Brugola (founded 1926). In 1946, Egidio Brugola patented an essential variation with a spiral shank.
The phrase “hex-head” is often used to describe this type of drive, however it is not compatible with its more common meaning, which refers to external-wrenching hexagons.
Sizing
Hex keys are measured across-flats (AF), which is the distance between two opposing (parallel) sides of a hexagon.
Variants
Tamper-resistant hex screws contain a projecting pin in the center of the hex recess that prevents normal hex keys from being inserted as a result, they can only be secured and removed with a special key with a recess for the pin. Torx screws also incorporate a similar “center pin reject” security mechanism.
Some hex keys feature rounded ends that allow them to be used at an angle from the screw. Bondhus Corporation designed this sort of hex key in 1964, and several businesses now manufacture it.
While providing access to previously inaccessible screws, thinning the tool shaft to create the rounded shape makes it weaker than the straight-shaft version, limiting the torque that can be applied; additionally, the rounded end only makes point contact with the screw, as opposed to the line contact made by straight-shaft keys.