When did hex bolts come out?

Driver for hexagonal socketed bolts or screws

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Hex keys of various sizes

A hex key (also, hex wrench, Allen key and Allen wrench or Inbus) is a simple driver for bolts or screws that have heads with internal hexagonal 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 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.[1]

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" name is a registered trademark (circa ) of the Allen Manufacturing Company (now Apex Tool Group) of Hartford, Connecticut; regardless, "Allen key" and "Allen wrench" are often seen as generic trademarks.

History

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The idea of a hex socket screw drive was probably conceived as early as the s to the s, but such screws were probably not manufactured until around . Rybczynski () describes a flurry of patents for alternative drive types in the s to the s in the U.S.,[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 because of the difficulties and expense of doing so at the time.

P. L. Robertson of Milton, Ontario, first commercialized the square socket in , having perfected and patented a suitable cold forming method, using the right material and the right die design. In &#;, William G. Allen also 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 the Allen Manufacturing Company of Hartford, Connecticut, exist from .[3]

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 . From this came the Unbrako line of products. This account from Hallowell does not mention the Allen patent of 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 screws and followed by cap screws. This was an industrial safety campaign, part of the larger Progressive Movement, to get headless set screws onto the pulleys and shafts of the line shafting 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.

Allen Manufacturing Company Inc advertisement for the Allen Safety Set Screw, a brand of set screw, in the Automobile Trade Directory, January

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 screws of square-socket drive from Britain, but they were very expensive.[5] (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 led to SPS's foray into fastener sales (for which it later became well known within the metalworking industries). Hallowell said "[for] a 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 [the U.S.]. Then we decided to incorporate a hexagon socket into the screw [&#;]."[6] 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 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.

Hallowell said that acceptance of the internal-wrenching hexagon drive was slow at first but that it eventually caught on quite strongly.[7] 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 "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 sure that the old-timers who read this book will remember this period vividly."[8] (These transitional growing pains echo those experienced many decades later with the adoption of the Torx 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 "Cap screws and setscrews with heads recessed to take hexagonal-bar wrenches are coming into increasing use.")[9]

Features

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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

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Cap head screws of various sizes Button head screws

Hex keys are best known as "Allen keys" or "Allen wrenches" in English-speaking countries like the UK, Australia, Canada and the U.S. and in Spanish-speaking countries such as Spain and Mexico (The "Allen" name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut, circa .[1] The brand is now owned by Apex Tool Group, LLC, which was acquired by Bain Capital in ).

In Germany the term "INBUS" is a registered trademark, originally an acronym for Innensechskantschraube Bauer und Schaurte, introduced in by the German company Bauer & Schaurte, in acquired by INBUS IP GmbH, Breckerfeld, Germany). INBUS IP GmbH was registered with the stated purpose of holding and licensing the trademark INBUS. In late to early , the company sent out desist orders to companies using the name "Inbus" for hex keys.[10][11][12] Hex keys with the INBUS brand are now manufactured at HaFu Werkzeugfabrik H. J. Fuhrmann GmbH, Breckerfeld, North Rhine-Westphalia, as of accounting for 7% of the company's EUR 8 million turnover[13] and as "Unbrako" key or wrench in Scandinavia (originally a Pennsylvania company established in , in acquired by Deepak Fasteners Limited).[14] In Italy, it is known as brugola, for the company Officine Egidio Brugola (established ). In Egidio Brugola patented an important variant with a spiral shank.

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

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Hex keys are measured across-flats (AF), which is the distance between two opposite (parallel) sides of the hexagon.[15]

Metric

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Metric hex key set with sizes from 1.5 mm to 10 mm

Standard metric sizes are defined in ISO : "Assembly tools for screws and nuts&#;Hexagon socket screw keys",[16] also known as DIN 911.[17]

Common metric hex key sizes

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Metric
(mm) US Customary Conversion
(in) Substitution
(in) 0.7 0.028 0.9 0.035 1.3 0.051 1.5 0.059 2 0.079

5

&#;

64

2.5 0.098 3 0.118 4 0.157

5

&#;

32

5 0.197 6 0.236 8 0.315

5

&#;

16

10 0.394 12 0.472 14 0.551 17 0.669 19 0.748

3

&#;

4

The full set of defined sizes are:[16]

• 0.7 mm, 0.9 mm, 1.3 mm
• 1.5 to 5 mm in 0.5 mm increments
• 5 mm 19 mm in 1 mm increments
• 21 mm, 22 mm, 23 mm, 24 mm, 27 mm, 29 mm, 30 mm, 32 mm, and 36 mm.

US customary

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Illustration of the largest (left) and smallest (right) hex keys that can be used with a given hex screw (middle) Security hex key

Hex key sizes in the U.S. are defined in ANSI/ASME standard B18.3- "Socket Cap, Shoulder, and Set Screws (Inch Series)".

Common US customary hex key sizes US Customary
(in) Metric Conversion
(mm) Substitution
(mm) 0.028 0.711 0.7 0.035 0.889 0.9 0.050 1.270 1.3

1

&#;

16

1.588

5

&#;

64

1.984 2

3

&#;

32

2.381

7

&#;

64

2.778

1

&#;

8

3.175

9

&#;

64

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3.572

5

&#;

32

3.969 4

3

&#;

16

4.763

7

&#;

32

5.556

1

&#;

4

6.350

5

&#;

16

7.938 8

3

&#;

8

9.525

Variants

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Hex keys of various sizes with ball ends

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 screws.

Some hex keys have a rounded end, allowing them to be used at an angle off-axis to the screw. This type of hex key was invented in by the Bondhus Corporation[19] and is manufactured by several companies. While providing access to otherwise inaccessible screws, thinning of the tool shaft to create the rounded shape renders it weaker than the straight-shaft version, limiting the torque that can be applied; in addition, the rounded end only makes point contact with the screw as opposed to the line contact made by straight-shaft keys.

Manufacturing methods

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Hex socket screw heads are usually made by stamping the head with a die, plastically deforming the metal. Other ways to generate the hex socket include linear broaching and rotary broaching. Broaching the heads with a linear broach is essentially the metalworking analog of mortising wood with a mortising 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 drawing die), then bending and shearing.

See also

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References

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Bibliography

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Pulished on Oct. 09,

The introduction and widespread use of nuts and bolts is the result of innovations in engineering and metallurgical technology. Hexagon nuts and bolts and the tools to use them require strict tolerances. As a standard fastener type, hexagon nuts and bolts are commonly used only after forging, stamping, and machining techniques have been developed before precise hex bolts can be manufactured.

The ancient screw

Hex nuts and bolts are part of a fastening system using threads. The thread's history can be traced back to the seventh century BC when the Assyrian king Sennacherib. Sennacherib uses screws as part of the pump that supplies water to the Hanging Gardens of Babylon's water supply system. The Greek mathematician Archytas of Tarentum described wood threads in the third century BC, and by the first century BC wood screws were widely used in oil and wine presses. These are usually attached to some kind of permanent handle as a rotating device.

Metal screws

Metal screws and bolts first appeared in Europe in the s but did not become common fasteners until the 18th century, when machine tools were developed to make them. Between and , Jesse Ramsden, an English musical instrument maker, Henry Maudslay, an English engineer, and David Wilkins, an American inventor, all obtained patents for thread cutting lathes, which were used to make screw rods. Early screws were often customized with square bolt heads. Replacement bolts are custom made, so they are not in large quantities and cannot be widely used.

Standardization

Square-head bolts were common in early applications because they were easier to make using the tools, metals, and techniques of the time. The precision of the square head is low, so the wrench may not be the exact size of the bolt, but it is close enough to turn the manual square head. But the square head is large and requires more rotation space. By , Joseph Whitworth, a British toolmaker, and his American counterpart, William Sellers, of the Franklin Institute, had proposed a standardized thread system. As toolmakers developed new technologies for mass production, standardized bolts and nuts were soon available.

Bessemer

Between and , the English metallurgist Sir Henry Bessemer developed the Bessemer process, which produced cheap mild steel in large quantities. Square bolt heads are easier to make when machinists use cast iron and thicker steel. However, as the machinery became smaller and more compact, hex bolts were developed to meet the demand for more compact bolt heads.

A large number of production

In , James Nasmyth, an assistant of Henry Maudslay, designed pioneering milling accessories for his desktop lathes and made a number of hexagonal bolts for a scale model built by the Science Museum in London. By the s, cold heads could be used to press the metal. It was not until the s that the Bessemer steel plant began to produce new mild steel of accurate thickness and quantity, and then the cool-machine began to press the hexagon nuts. This innovation means that nuts stamped from flat metal billets and machined to exact tolerances can be screwed to bolts made by the new screw machine in factories anywhere in the country. In heavy industrial applications, larger hexagon nuts quickly replace square bolt heads.

Wars

During the two wars of the 20th century, the huge military equipment and equipment maintenance forced manufacturers of war materials to achieve higher standards. The humble hexagon bolt and nut fastener system are vital not only to the war effort but to every aspect of modern life.

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