Fact Checked

What is a Hex Key?

Maggie Worth
Maggie Worth

A hex key is a tool used to tighten and loosen a screw or bolt, that has a hexagonal depression in its head. The tool may also be called a hex wrench, Allen wrench, hex-head key, zeta wrench, Alum wrench, or Inbus key. These are used in both consumer and industrial assembly, but are often associated with self-assembly kits sold to consumers, particularly furniture kits.

The first hex key was developed in 1911. The tools came into common use during the manufacturing boom of World War II. The Allen Manufacturing Company obtained the first patent in 1943, and its model became so popular that the brand name Allen wrench is frequently used to refer to any such tool, even those manufactured by other companies.

Hex keys.
Hex keys.

The term 'hex' comes from hexa, the Greek word for 'six.' The tool is made of a six-sided strip of metal that is bent at a 90° angle about one-third of the way from one end. Usually, the short side is inserted into the fastener, while the long side provides a hand-hold for the user, but most hex wrenches are reversible. The user rotates the key to turn the screw or bolt. The amount of torque, or force, that the tool can apply depends on the length and thickness of the hex key.

Ball end hex keys.
Ball end hex keys.

Fasteners with hex heads are often easier to turn than those with Phillips heads or standard screwdriver slots. The six points of contact allow the hex key to fit more snugly into the fastener head than is possible with a screwdriver. This helps prevent the tool from slipping out of the fastener head. In addition, the design of hex-head fasteners makes them less likely to strip out, or distort the head, than standard or Phillips head fasteners.

A socket-head cap screw, which is used with a hex key.
A socket-head cap screw, which is used with a hex key.

Hex wrenches must be used manually, as no drill attachments are available. Further, they can be difficult to maneuver in tight places because of the space needed to turn the handle of the key. Despite these drawbacks, the tool remains a light, simple, inexpensive solution for many consumer and industrial situations.

Hex keys are often purchased in sets of varying sizes. They are packaged in self-assembly furniture kits because they are small, inexpensive to manufacture, and easy to use. Inclusion in such kits prevents the user from having to find a screwdriver or drill in order to complete the project, and is thought to increase customer satisfaction with the assembly process.

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Discussion Comments


@hamje32 - Like you, the only hex keys I have lying around are those that have come with kits of one kind or another. I’ve never bought a hex key set yet.

I do wish, however, that more things around the house were made with hex nuts instead of Phillips screws. The hex bolts are far, far easier to turn.

Last year I did a bathroom project where I had to remove a shower head, and it was screwed in with a regular Phillips screw. For the life of me, I couldn’t unloosen it. Maybe the threads were too bare or something but my screwdriver kept slipping.

Finally I had to hire a guy to come in and do it; he had some special tools to pry it loose. Had that shower head been locked in place with a hex bolt, I could have saved some money.


Most of my furniture is stuff I’ve built myself, from kits obtained from the store. You can guess that it’s probably not high quality but it is easy to assemble.

One of the things that makes it easy is the hex wrench that they always supply with the kit. Sometimes they supply other tools too, but this is the most common one.

It’s always such a relief not to have to dig around in my toolkit in order to assemble the kit. I like the hex wrench because even though it’s small, it fits the hex nuts perfectly, and the wrench enables me to apply just the right amount of torque to get a good, secure fit.

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    • Hex keys.
      Hex keys.
    • Ball end hex keys.
      Ball end hex keys.
    • A socket-head cap screw, which is used with a hex key.
      A socket-head cap screw, which is used with a hex key.