Hex Keys and Allen Wrenches

Using Allen Wrenches

and Hex Keys for

Allen and Hex Bolts


The Seventh Wonder of the Tool World: Hex Keys & Allen Wrenches
By: The Working Man

Most people, at least if they are home handymen or work in
construction or mechanical trades, know that a Hex or Allen
bolt is a bolt with an inset hexagonal socket for tightening
or loosening it. An Allen Wrench is an "L" shaped six-sided
wrench that in cross section has a hexagonal shape, hence
the name Hex Key.

The tools that are used for tightening and loosening a Hex
Bolt are the Allen Wrenches, also known as Hex Keys, Zeta
wrenches, or Unbrako Keys. The short side of the "L" is
pressed down into the recess on the bolt head and the longer
side is used as a lever to turn the wrench and so the bolt.
Some special usage hex keys have a "T" handle on the end to
provide more torque.

One of the original manufacturers of this type of bolt in
the United States called their inset head screws "Unbrako"
(unbreakable), and later during World War II the Allen
Manufacturing Company of Hartford, Connecticut trademarked
their very popular line of hex wrenches as Allen wrenches.

Eventually Allen wrench became the defacto common name for
the hex wrench, despite the fact that the "Unbrako" was
actually the first on the scene. The "Zeta" name is because
zeta is the sixth letter of the Greek alphabet.

Allen Wrenches come in various sizes to match standard hex
bolt sizes, and are often purchased as a set of each size
that is mounted on a ring or into a case so the wrenches
remain together and are not so easily lost.

Hex bolts were developed so that the contact surface is less
likely to be damaged. The six sides of the inset give more
contact with the driver and make stripping the bolt or
slipping of the wrench almost impossible.

Advantages of the Allen system include the fact that the
small size of the key reduces potential damaging torque. The
tools are small and easily carried, the use of very small
bolt heads is possible, and the wrench can be used to place
the bolt into its socket if needed. Also, either end of the
Allen wrench can be used for the best torque and reach.

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