Hex keys of various sizes
Socket head screws of various sizes
A hex key (also, hex wrench, Allen key and Allen wrench) is a simple driver for bolts or
screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
s that have heads with ''internal''
hexagon
In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.
Regular hexagon
A '' regular hexagon'' has ...
al recesses (sockets).
Hex keys are formed from a single piece of hard hexagonal steel rod, having blunt ends that fit snugly into similarly-shaped screw sockets. The rods are bent to 90º, forming two arms of unequal length resembling an "L". The tool is usually held and twisted by its long arm, creating a relatively large
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
at the tip of the short arm; it can also be held by its short arm to access screws in difficult-to-reach locations and to turn screws faster at the expense of torque.
Hex keys are designated with a socket size and are manufactured with tight tolerances. As such, they are commonly sold in kits that include a variety of sizes. Key length typically increases with size, but not necessarily proportionally so.
Variants on this design have the short end inserted in a transverse handle, which may contain multiple keys of varying sizes that can be folded into the handle when not in use.
While often used in
generic terms for "hex key", the "
Allen Allen, Allen's or Allens may refer to:
Buildings
* Allen Arena, an indoor arena at Lipscomb University in Nashville, Tennessee
* Allen Center, a skyscraper complex in downtown Houston, Texas
* Allen Fieldhouse, an indoor sports arena on the Unive ...
" name is a registered trademark (circa 1910) of the
Allen Manufacturing Company (now
Apex Tool Group) of
Hartford
Hartford is the capital city of the U.S. state of Connecticut. It was the seat of Hartford County until Connecticut disbanded county government in 1960. It is the core city in the Greater Hartford metropolitan area. Census estimates since the ...
,
Connecticut
Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its cap ...
; regardless, "Allen key" and "Allen wrench" are often seen as
generic trademark
A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products or ...
s.
History
The idea of a hex ''socket'' screw drive was probably conceived as early as the 1860s to the 1890s, but such screws were probably not manufactured until around 1910. Rybczynski (2000) describes a flurry of patents for alternative drive types in the 1860s to the 1890s in the US,
[.] which are confirmed to include ''internal''-wrenching square and triangle types (that is, square and triangular sockets) (), but he explains that these were patented but not manufactured because of the difficulties and expense of doing so at the time.
P. L. Robertson
Peter Lymburner Robertson (December 10, 1879 – September 28, 1951) was a Canadian inventor, industrialist, salesman, and philanthropist who popularized the square-socket drive for screws, often called the Robertson drive. Although a square-socke ...
, of
Milton,
Ontario
Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
,
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, first commercialized the ''square'' socket in 1908, having perfected and patented a suitable
cold forming
In metallurgy, cold forming or cold working is any metalworking process in which metal is shaped below its recrystallization temperature, usually at the ambient temperature. Such processes are contrasted with hot working techniques like hot r ...
method, using the right material and the right die design.
In 1909–1910, William G. Allen also patented a method of cold-forming screw heads around a ''hexagonal'' die (). Published advertisements for the "Allen safety
set screw
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which distingu ...
" by the Allen Manufacturing Company of Hartford, Connecticut, exist from 1910.
In his autobiography, the founder of the Standard Pressed Steel Company (SPS; now SPS Technologies, Inc.), Howard T. Hallowell Sr. presents a version of events
[.] in which SPS developed a hex socket drive in-house, independently of Allen, circa 1911. From this came the line of products. This account from Hallowell does not mention the Allen patent of 1910, nor the Allen safety set screw product line. Hallowell does describe, however, the same inspiration also mentioned in connection with Allen for a wave of adoption of the hex socket head, beginning with
set screw
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which distingu ...
s and followed by
cap screw
A screw and a Bolt (fastener), bolt (see ''#Differentiation between bolt and screw, Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helix, helical ridge, called a ''m ...
s. This was an industrial safety campaign, part of the larger
Progressive Movement
Progressivism holds that it is possible to improve human societies through political action. As a political movement, progressivism seeks to advance the human condition through social reform based on purported advancements in science, techn ...
, to get headless set screws onto the pulleys and shafts of the
line shaft
A line shaft is a power-driven rotating shaft for power transmission that was used extensively from the Industrial Revolution until the early 20th century. Prior to the widespread use of electric motors small enough to be connected directly to e ...
ing that was ubiquitous in factories of the day. The headless set screws would be less likely to catch the clothing of workers and pull them into injurious contact with the running shaft.
left, Allen Manufacturing Company Inc advertisement for the Allen Safety Set Screw, a brand of
set screw, in the Automobile Trade Directory, January 1913
SPS at the time was a prominent maker of shaft hangers and
collars, the latter of which were put in place with set screws. In pursuit of headless set screws with a better drive than a straight slot, Hallowell said, SPS had sourced
set screw
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which distingu ...
s of square-socket drive from
Britain
Britain most often refers to:
* The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands
* Great Britain, the largest island in the United King ...
, but they were very expensive. (This was only 2 years after Robertson's Canadian patent.) This cost problem drove SPS to purchase its first
screw machine and make its screws in-house, which soon led to SPS's foray into fastener sales (for which it later became well known within the metalworking industries). Hallowell said that "
ora while we experimented with a screw containing a square hole like the British screw but soon found these would not be acceptable in this country
he U.S.
He or HE may refer to:
Language
* He (pronoun), an English pronoun
* He (kana), the romanization of the Japanese kana へ
* He (letter), the fifth letter of many Semitic alphabets
* He (Cyrillic), a letter of the Cyrillic script called ''He'' i ...
Then we decided to incorporate a hexagon socket into the screw
" Hallowell does not elaborate on ''why'' SPS found that the square hole "would not be acceptable in this country", but it seems likely that it would have to have involved licensing Robertson's patent, which would have defeated SPS's purpose of driving down its cost for internal-wrenching screws (and may have been unavailable at any price, as explained at "
List of screw drives > Robertson"). The story, if any, of whether SPS's methods required licensing of Allen's 1910 patent is not addressed by Hallowell's memoir. The book does not mention which method—cold forming or linear broaching—was used by SPS in these earliest years. If the latter was used, then Allen's patent would not have been relevant.
Soon after SPS had begun producing the
exsocket head set screw, Hallowell had the idea to make a
exsocket head cap screw (SHCS). Hallowell said, "Up to this moment none of us had ever seen a socket head cap screw, and what I am about to relate concerns what I believe was the first socket head cap screw ever made in this country
he U.S.
He or HE may refer to:
Language
* He (pronoun), an English pronoun
* He (kana), the romanization of the Japanese kana へ
* He (letter), the fifth letter of many Semitic alphabets
* He (Cyrillic), a letter of the Cyrillic script called ''He'' i ...
" SPS gave their line of screws the Unbrako brand name, chosen for its echoing of the word ''
unbreakable
Unbreakable may refer to:
* '' Unbreakable: My Story, My Way'', a book written by Jenni Rivera
* Unbreakable (horse) (1935–1962), a Thoroughbred racehorse and sire
Film and television
* ''Unbreakable'' (film series), a trilogy directed by M ...
''.
Hallowell said that acceptance of the internal-wrenching hexagon drive was slow at first (painfully slow for SPS's sales), but that it eventually caught on quite strongly. This adoption occurred first in
tool and die work and later in other manufacturing fields such as defense (aircraft, tanks, submarines), civilian aircraft, automobiles, bicycles, furniture and others.
Concerning the dissemination of the screws and wrenches, Hallowell said that "the transition from a square head set screw
allowell refers here to the then-ubiquitous external-wrenching square driveto a hexagon socket head hollow set screw
for which had to be developed special keys or wrenches for tightening or loosening the screw, was the cause of more profanity among the mechanics and machine manufacturers than any other single event that happened.
I am sure that the old-timers who read this book will remember this period vividly." (These transitional growing pains echo those experienced many decades later with the adoption of the
Torx
Torx (pronounced ) is a trademark for a type of screw drive characterized by a 6-point star-shaped pattern, developed in 1967, Bernard F. Reiland, "Coupling arrangement and tools for same", filed 1967-03-21 by Camcar Textron. A popular generic ...
drive).
World War II, with its unprecedented push for industrial production of every kind, is probably the event that first put most laypersons in contact with the internal-wrenching hexagon drive. (''Popular Science'' magazine would note in 1946 that "Cap screws and setscrews with heads recessed to take hexagonal-bar wrenches are coming into increasing use.")
[.]
Features
Same hex key, different screw threads
Some features of hex keys are:
* The tool is simple, small and light.
* The contact surfaces of the screw or bolt are protected from external damage.
* There are six contact surfaces between bolt and driver.
* Very small bolt heads can be accommodated.
* The tool allows the use of headless and recessed-head screws.
* The screw can be held by the key while it is inserted into its hole.
* The torque applied to the screw is constrained by the length and thickness of the key.
* The tool is cheap to manufacture, so it can be included with products requiring end-user assembly.
* Either end of the tool can be used to take advantage of reach or torque.
* The tool can be reconditioned by grinding the worn-out end.
Nomenclature
The term "hex key" is best known as "
Allen Allen, Allen's or Allens may refer to:
Buildings
* Allen Arena, an indoor arena at Lipscomb University in Nashville, Tennessee
* Allen Center, a skyscraper complex in downtown Houston, Texas
* Allen Fieldhouse, an indoor sports arena on the Unive ...
" in the
English-speaking countries
The following is a list of English-speaking population by country, including information on both native speakers and second-language speakers.
List
* The European Union is a supranational union composed of 27 member states. The total En ...
like UK, Australia, Canada and the USA (The “Allen” name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut circa 1910, now owned by Apex Tool Group, LLC, which was acquired by
Bain Capital
Bain Capital is an American private investment firm based in Boston. It specializes in private equity, venture capital, credit, public equity, impact investing, life sciences, and real estate. Bain Capital invests across a range of industry se ...
in 2014), and also in Spain (''llave Allen'' pronounced with
Spanish double L, ).
In Germany the term "INBUS" is a registered trademark, originally an acronym for ''Innensechskantschraube Bauer und Schaurte'', introduced in 1934 by the German company Bauer & Schaurte, in 2015 acquired by INBUS IP GmbH,
Breckerfeld
Breckerfeld is a town in the district of Ennepe-Ruhr-Kreis, in North Rhine-Westphalia, (Germany). It is located in the southeasternmost part of the Ruhr area in northern Sauerland. The town is a member of Regionalverband Ruhr (association).
Ge ...
, Germany). INBUS IP GmbH was registered with the stated purpose of holding and licensing the trademark INBUS. In late 2015 to early 2016, the company sent out desist orders to companies using the name "Inbus" for hex keys. Hex keys with the INBUS brand are now manufactured at HaFu Werkzeugfabrik H. J. Fuhrmann GmbH, Breckerfeld, North Rhine-Westphalia, as of 2017 accounting for 7% of the company's EUR 8 million turnover.
and as "Unbrako" key or wrench in Scandinavia (originally a Pennsylvania company established in 1911, in 2008 acquired by Deepak Fasteners Limited). In Italy, it is known as ''brugola'', for the company Officine Egidio Brugola (established 1926).
The term "hex-head" is sometimes used to refer to this type of drive, but this use is not consistent with its more conventional use referring to external-wrenching hexagons.
Sizing
Hex keys are measured across-flats (AF), which is the distance between two opposite (parallel) sides of the hexagon.
Metric sizes
Standard metric sizes are defined in
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
2936:2014 "Assembly tools for screws and nuts—Hexagon socket screw keys", also known as
DIN 911, and, measured in millimeters (mm) are:
*0.7, 0.9, 1.0, 1.25, 1.3, 1.5
*2 to 6 in 0.5 mm increments
*7 to 22 in 1 mm increments
* 24, 25, 27, 30, 32, 36, 42 and 46 mm.
![Screw Size vs Allen Key Size](https://upload.wikimedia.org/wikipedia/commons/2/22/Screw_Size_vs_Allen_Key_Size.jpg)
Metric hex keys are sometimes designated using an "M" followed by their size in millimetersfor example, "M6" for 6 mm across flatswhich can cause confusion due to similarity with the
ISO "M" nomenclature for metric screws.
US customary sizes
Hex key sizes in the US are defined in
ANSI
The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
/
ASME
The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...
standard B18.3-1998 "Socket Cap, Shoulder, and Set Screws (Inch Series)".
Variants
![Allen wrench with ball end 1](https://upload.wikimedia.org/wikipedia/commons/6/69/Allen_wrench_with_ball_end_1.jpg)
Tamper-resistant hex screws have a protruding pin in the center of the hex recess that prevents insertion of standard hex keys; as such, they can only be fastened and removed with a special key that has a recess for the pin. A similar "center pin reject" security feature is also used on
TORX
Torx (pronounced ) is a trademark for a type of screw drive characterized by a 6-point star-shaped pattern, developed in 1967, Bernard F. Reiland, "Coupling arrangement and tools for same", filed 1967-03-21 by Camcar Textron. A popular generic ...
screws.
Some hex keys have a ball on one end, allowing them 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 screws, 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; in addition, the ball end only makes point contact with the screw as opposed to the line contact made by straight-shaft keys.
Manufacturing methods
Hex socket screw heads are usually made by stamping the head with a
die
Die, as a verb, refers to death, the cessation of life.
Die may also refer to:
Games
* Die, singular of dice, small throwable objects used for producing random numbers
Manufacturing
* Die (integrated circuit), a rectangular piece of a semicondu ...
, plastically deforming the metal. Other ways to generate the hex socket include
linear broaching and
rotary broaching
Broaching is a machining process that uses a toothed tool, called a broach, to remove material. There are two main types of broaching: ''linear'' and ''rotary''. In linear broaching, which is the more common process, the broach is run linearly ...
. Broaching the heads with a linear broach is essentially the metalworking analog of mortising wood with a
mortising machine
A mortiser or morticer is a specialized woodworking machine used to cut square or rectangular holes in a piece of lumber (timber), such as a mortise in a mortise and tenon joint.
Square chisel mortiser
The square chisel mortiser (also called '' ...
; a hole is drilled and then the corners are broached out. This operation often leaves little telltale curled chips still attached at the bottom of the socket. These are negligible for most applications.
Hex keys are made by imparting the hexagon cross-section to steel wire (for example, with a
drawing
Drawing is a form of visual art in which an artist uses instruments to mark paper or other two-dimensional surface. Drawing instruments include graphite pencils, pen and ink, various kinds of paints, inked brushes, colored pencils, crayons, ...
die), then bending and shearing.
See also
*
Wrench
A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning.
In the UK, Ireland, Australia, and New Zeala ...
*
List of screw drives
At a minimum, a screw drive is a set of shaped cavities and protrusions on the screw head that allows torque to be applied to it. Usually, it also involves a mating tool, such as a screwdriver, that is used to turn it. The following heads are ca ...
References
Bibliography
*
*
*
External links
Hex Keys (Allen Keys) and Bits Sockets Dimensions
{{Bicycle tools
Bicycle tools
Mechanical hand tools
Screws
American inventions