Hex key

Allen ( in German commonly under the brand name Allen) is a carrier profile for screws with a hexagon socket in the screw head. The corresponding wrench with outside hexagon profile is called an Allen key. In many countries the Allen screw on the organization, Allen Manufacturing Company (Hartford, Connecticut) Allen screw, the allen wrench Allen key or Allen wrench is called.

Brand Name Allen

The acronym stands for Allen " Allen screw Bauer and Schaurte ". Often, the name is pronounced by assimilation, contrary to the spelling " allen ". The name is derived from the initial manufacturer Bauer & Schaurte (up to 1980 in Neuss ). Both the company and the Allen brand today belong to the Whitesell Group.

Development and Technology

Bauer & Schaurte let this screw type patented in 1936 in Germany and brought them to market. The technique was, among other things, developed and perfected by Walter Beduwé, then a senior engineer. The invention of the Allen screw goes well back to the year 1911.

In this type of screw is an Allen sunk in a cylindrical screw head. Compared with the hexagon head screw ( with external hex head) less space for the head is needed. Compared to an equal-sized Phillips screw, an allen screw absorb about ten times the torque.

Properties and applications

Allen screws are well suited for screw connections where the screw heads are by design difficult to access. It is sufficient if the head can be accessed from above, for example through a hole whose diameter is greater than the width across corners of the respective key. With keys whose tip is ground spherical, the screws can also tighten and loosen when key and screw are not aligned. Allen screws which can be contacted sink to save space, if protruding screw heads interfere.

Inbusschlüsselsätze are inexpensive and compact in size. In addition, Allen key can be easily extended with a tube to produce higher tightening or loosening torques. These properties make the Allen screw therefore the preferred screw in special machines.

On Bicycle Allen screws are often used, because this tool kit can be kept small. The inexpensive Allen key can be cost-saving added by the manufacturer even with kits, eg for furniture. The socket head screw with hexagon socket is characterized by a pleasing appearance, which is why it is often used for ornamental purposes. In commodities, the round shape has the advantage that few parts or textiles can hook up to it and the risk of injury is lower.

A disadvantage of the hexagon socket at the outdoor use is to be able to accumulate dirt and water in the cavity and lead to corrosion. In addition, the screw head is inherently higher than that of a hex bolt, but also narrower in diameter.

Meanwhile, there are screw driving systems which allow compared to Allen a better transfer of the tightening torque on the screw and allow higher torques, for example Torx from the USA or multi-tooth triple square to DIN 34824th


Socket head cap screws are available in various designs, which are also described in standards. The most common mechanical engineering allen screws are listed in the following standards:

  • EN ISO 4026 ( formerly DIN 913): Set screw with hexagon socket and flat point
  • EN ISO 4027 ( formerly DIN 914): Set screw with hexagon socket and tip
  • EN ISO 4028 ( formerly DIN 915 ): Set screw with hexagon socket and spigot
  • EN ISO 4029 ( formerly DIN 916): Set screw with hexagon socket and cup point
  • EN ISO 4762 ( formerly DIN 912): Cylinder head screw with hexagon socket
  • EN ISO 10642 ( formerly DIN 7991 ): countersunk screw with hexagon socket
  • DIN 7984: Cylinder head screw with low head and hexagon socket
  • DIN 6912: Cylinder head screw with low head, key management and internal hexagon

Should the above Ausführungenen listed in the technical documentation, the name by the relevant standard shall be used. The name Allen screw is colloquial. The size specification of Allen refers to the perpendicular distance in millimeters between two parallel sides of its hexagonal cross -section, which is also known as key length, abbreviated SW,.

Allen wrench size SW, suitable for screw sizes ( outer thread diameter )

Similar head connector molds for screwdriver

The rarer inner pentagonal screws are used by some car manufacturers, incorporated, inter alia, for the brakes, instead of hex screws. The mating internal pentagon keys are available from specialist dealers.

An inner pentagon is also used as anti-theft device for quick releases in bike technology, but these fortifications lose sight of their true quick-release character. The clamping lever is replaced by a peelable inner pentagonal pin must then be carried by the driver.

Also in the automotive industry is the internal serration ( triple square ) application, if particularly high torques are required, for example in the drive shafts in the drive train.