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A hex key orAllen key or wrench (also known by various
othersynonyms) is atoolofhexagonalcross-section used to
drive bolts andscrewsthat have a hexagonal socket in the head
(internal-wrenching hexagon drive).
TheAllen name is a registered trademark, originated by theAllen
Manufacturing CompanyofHartford,
Connecticutcirca 1910, and currently owned byApex Tool Group,
LLC. Itsgenericized useis discouraged by this
company. The standard generic name used in catalogs and
published books and journals is "hex key".
Contents
[hide]
1 Nomenclature
2 Features
3 History
4 Hex key standard sizes
o 4.1 Variants
5 Manufacturing methods
6 References
7 Bibliography
[edit]Nomenclature
The term "hex key" has various synonyms. Some are explained by
the geographical and commercial history of the drive
type's development (as detailed in thehistorysection); these
includeAllen,Unbrako, and Inbuskey or wrench. The
synonym zetakey or wrench refers to thesixth letter of the Greek
alphabet. The term hex-headis sometimes used to
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refer to this type of drive, but this use is not consistent with
its more conventional use referring to external-wrenching
hexagons.
In the fastener industry, the terms socket headorhex socket
headare generally used for the driven part of the driver
driven pair. A less common synonym isfemalehex.
[edit]Features
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.
The tool can be used with a headless screw.
The screw can be inserted into its hole using the key.
Torqueis constrained by the length and thickness of the key.
Very small bolt heads can be accommodated.
The tool can be manufactured very cheaply, so one is often
included with products requiring end-user assembly.
Either end of the tool can be used to take advantage of reach or
torque.
The tool is L-shaped[1]
[edit]HistoryExtant records suggest (without offering exhaustive
documentation) that the idea of a hex socket screw drive was
probably conceived as early as the 1860s through 1890s, but that
such screws were probably not manufactured until
around 1910. Rybczynski (2000) describes a flurry of patents for
alternative drive types in the 1860s through 1890s in the
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US,[2]
which are confirmed to include 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 manufactured due to the difficulties and expense
of doing so at the time.P. L. Robertson, of Milton, Ontario,
Canada, first commercialized the square socket in 1908,
having perfected and patented a manufacturing method
(cold-forming, using the right material and the right die
design).In 19091910, William G. Allen patented a method of
cold-forming screw heads around a hexagonal die (U.S. Patent
960,244). Published advertisements for the "Allen safety set
screw" by theAllen Manufacturing Companyof Hartford,
Connecticut, exist from 1910.[3]
Although it is unlikely that Allen was the first person to think
of a hex socket drive, his
patent for a manufacturing method and his realized product
appear to be the first.
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[4]
in which SPS developed a hex socket drive in-house,
independently of
Allen, circa 1911. From this came the Unbrako 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 withset screwsand
followed by cap screws. This was an industrial safety campaign,
part of the largerProgressive Movement, to get
headless set screws onto the pulleys and shafts of theline
shaftingthat 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.
SPS at the time was a prominent maker of shaft hangers
andcollars, the latter of which were set in place with set
screws. In pursuit of headless set screws with a better drive
than a straight slot, Hallowell said, SPS had sourcedset
screwsof square-socket drive from England, but they were very
expensive.[5]
(This was only 2 years after Robertson's
Canadian patent.) This cost problem drove SPS to purchase its
firstscrew machineand 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).
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Hallowell said that "[for] a while we experimented with a screw
containing a square hole like the English screw but soon
found these would not be acceptable in this country [the U.S.].
Then we decided to incorporate a hexagon socket into the
screw []."[6]
Hallowell does not elaborate on whySPS 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
defeatedSPS'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 methodcold forming or linear
broachingwas 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 [hex] socket head set
screw, Hallowell had the idea to make a [hex] socket
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 [the
U.S.]."[7]
SPS gave their line of screws the Unbrako brand name, chosen for
its echoing of the wordunbreakable.
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.[8]
This adoption occurred first intool and die workand 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 [Hallowell refers here to the then-ubiquitous
external-wrenching square drive] to 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
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sure that the old-timers who read this book will remember this
period vividly."[9]
(These transitional growing pains echo
those experienced many decades later with the adoption of
theTorxdrive).
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 Sciencemagazine would note in 1946 that"Cap screws and
setscrews with heads recessed to take hexagonal-bar wrenches are
coming into increasing use.")
[10]
It appears that the internal-wrenching hexagon drive may have
been independently reinvented in various countries. At
the least, the design (or methods of manufacturing it) was
patented in various countries by various patentees, and its
name varies. For example, in various European countries, it is
known by the name Inbus (often misspelled *Imbus), after
the company that patented them in Germany in 1936, Bauer und
Schaurte ofNeuss(Inbus stands
forInnensechskantschraube Bauerund Schaurte). Similarly, there
is another name in Italian (brugola), stemming from
an Italian company's name.
[edit]Hex key standard sizes
Hex keys are measured across-flats (AF), which is the distance
between two opposite (parallel) flat sides of the key.
Standard metric sizes are defined inISO2936:2001 "Assembly tools
for screws and nutsHexagon socket screw keys",
also known asDIN911, 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.
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Metric hex wrench sizes are sometimes referred to using the
designation "M" followed by the size in millimeters of the
tool or socket, e.g. "M6", although this may be confused with
the standard use of "M6" which refers to thethreads of a
metric screw or bolt.
American sizes are defined inANSI/ASMEstandard B18.3-1998
"Socket Cap, Shoulder, and Set Screws (Inch Series)".Values given
here are taken from Machinery's Handbook, 26th Edition, section
"Fasteners", chapter "Cap and Set
Screws", table 4 (p. 1601).
Screw size (nominal) Socket size (inches) Approximate socket
size (mm)
No. 6 7/64 2.78
No. 8 9/64 3.57
No. 10 5/32 3.97
1/4 3/16 4.76
5/16 1/4 6.35
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3/8 5/16 7.94
7/16 3/8 9.52
1/2 3/8 9.52
5/8 1/2 12.7
3/4 5/8 15.9
7/8 3/4 19.0
1 3/4 19.0
Note that numerous other sizes are defined; these are the most
common.
Using a hex wrench on a socket that is too large may result in
damage to the fastener or the tool. An example would be
using a 5 mm tool in a 5.5 mm socket. Because hex-style hardware
and tools are available in
bothmetricandBritish/Imperialsizes (with British sizes most
commonly used in theUnited Statesand denoted "SAE",
and metric in other places), it is also possible to select a
tool that is too small for the fastener by using a British-
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unit/Imperial tool on a metric fastener, or the converse. There
are some exceptions to that. For example, 4 mm keys are
almost exactly the same size as 5/32", and 8 mm keys are almost
exactly the same size as 5/16", which makes 4 mm
and 8 mmpreferred numbersfor consumer products such as
self-assembly particle-board furniture, because end users
can successfully use an imperial key on a metric fastener, or
vice versa, without stripping. 19 mm keys are so close to
the same size as 3/4" that they are completely interchangeable
in practical use.
[edit]Variants
Hex keys of various sizes with ball ends.
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. TheTORXhead'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 theBondhus Corporation,[11]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.
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[edit]Manufacturing methods
Hex socket screw heads are usually made by stamping the head
with adie, plasticly deforming the metal. Other ways
to generate the hex socket includelinear broachingandrotary
broaching. Broaching the heads with a linear broach isessentially
the metalworking analog of mortising wood with amortising machine;
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 die), then bending and
shearing.
http://en.wikipedia.org/w/index.php?title=Hex_key&action=edit§ion=6http://en.wikipedia.org/w/index.php?title=Hex_key&action=edit§ion=6http://en.wikipedia.org/w/index.php?title=Hex_key&action=edit§ion=6http://en.wikipedia.org/wiki/Die_(manufacturing)http://en.wikipedia.org/wiki/Die_(manufacturing)http://en.wikipedia.org/wiki/Die_(manufacturing)http://en.wikipedia.org/wiki/Broaching_(metalworking)http://en.wikipedia.org/wiki/Broaching_(metalworking)http://en.wikipedia.org/wiki/Broaching_(metalworking)http://en.wikipedia.org/wiki/Broaching_(metalworking)#Rotary_broachinghttp://en.wikipedia.org/wiki/Broaching_(metalworking)#Rotary_broachinghttp://en.wikipedia.org/wiki/Broaching_(metalworking)#Rotary_broachinghttp://en.wikipedia.org/wiki/Mortising_machinehttp://en.wikipedia.org/wiki/Mortising_machinehttp://en.wikipedia.org/wiki/Mortising_machinehttp://en.wikipedia.org/wiki/Mortising_machinehttp://en.wikipedia.org/wiki/Broaching_(metalworking)#Rotary_broachinghttp://en.wikipedia.org/wiki/Broaching_(metalworking)http://en.wikipedia.org/wiki/Die_(manufacturing)http://en.wikipedia.org/w/index.php?title=Hex_key&action=edit§ion=6
