Hex Key - History

History

Extant 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 US, 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 1909–1910, 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 the Allen Manufacturing Company of Hartford, Connecticut, exist from 1910. 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 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 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.

SPS at the time was a prominent maker of shaft hangers and collars, 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 sourced set screws of square-socket drive from England, 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 " 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 . 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 socket head set screw, Hallowell had the idea to make a 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 ." SPS gave their line of screws the Unbrako brand name, chosen for its echoing of the word unbreakable.

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 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." (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 1946 that "Cap screws and setscrews with heads recessed to take hexagonal-bar wrenches are coming into increasing use.")

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 of Neuss (Inbus stands for Innensechskantschraube Bauer und Schaurte). Similarly, there is another name in Italian (brugola), stemming from an Italian company's name.