What Is Allen Wrench? Types, Size, Uses

What Is Allen Wrench? Types, Size, Uses

Allen wrenches resemble hexagon-shaped keys and look like L-shaped devices. They have a multitude of uses. Including fastening screws into metal, plastic, and wood. Allen wrenches are very easy to use and beginner-friendly.

You’ll often see them included with flat-pack furniture that requires self-assembly. Allen keys come in several types which all have different uses.

We’ll cover more about Allen wrenches in this article, including what they are, the available different types of Allen wrenches, and their pros and cons. If you want to learn more about the Allen wrench and its uses, keep reading!

What Are Allen Wrenches?

Allen wrenches (also known as an Allen key or hex key) are devices used for driving screws and bolts with inner hexagon-shaped sockets. The wrenches tend to be made from strong steel rods that are also hexagonal-shaped.

They have blunt edges that fit into screw sockets of the same size. These steel rods are bent at a right angle so that either side has differing lengths, resembling the letter ‘L’.

The user would hold the wrench by the longer end, generating more torque at the end of the shorter side. The tools are made with the socket’s size in mind and produced with particularly firm tolerances. The wrenches are usually used to fix hex screws to metal, wood, and plastic.

Different Kinds Of Allen Wrenches

Allen wrenches are available in many different types, which we’ll cover below.


The L-style is the usual type of Allen wrench that you’d find at hardware stores and online. As the name suggests, the wrench looks like an L, allowing it to get into tighter areas and deliver better control whenever necessary.

There are two kinds of L-shaped Allen keys – short arm Allen keys and long arm Allen keys. L-style Allen wrenches are a good choice for those searching for a wrench set. The 1.5-10 millimeter option is a good all-rounder that suits a lot of tasks.


T-handle Allen wrenches let you spin the tool quickly and easily, delivering support when for standard tasks. T-handle hex keys are some of the most used wrenches used for bike mechanic tasks, as well as within the motorsport field.


P-handle tools are an updated form of L-style wrenches. These have a grip where the wrench bends which makes it sit comfortably in the hand. These Allen wrenches are often seen in expert workshops. 

Folding Hex Keys

The folding hex key has arm keys that fold inside a storage compartment. These folding hex handles are either plastic or metal, depending on personal choice or the task at hand.

Folding keys are usually used to deliver powerful torque, as they fold at right angles against the storage compartment handle.

The main benefit of this is that the keys will fold inwards at 180 degrees. This makes it easier for the user to reach fasteners that are difficult to access, allowing them to replace fasteners and screws quickly. A folding hex wrench is a popular choice for cyclists and motorbike riders.

Ratcheting Hex

These interesting tools are either in the form of a T handle or a folding handle, delivering lots of movement as a result. These often have screwdriver components that are attached to the handle with a magnetic holder.

This holder encases the entire tool. Ratcheting hex wrenches are ideal for electric drill drivers, which makes them great for managing rotor bolt tasks.

Torque Wrenches

These Allen wrenches are often used to deliver particular torque to fasteners, like lag screws, bolts, and nuts. They are like socket wrenches that have interesting mechanisms inside.

Torque wrenches are used for tasks that involve specific tightness of bolts or screws. These wrenches are important instruments in many workshops, particularly when working with delicate parts. Despite this, torque wrenches are not a replacement for hex wrenches.

What Is Allen Wrench? Types, Size, Uses

Allen Screwdrivers

Allen screwdrivers are used for tasks that require less torque and tight clearance. These resemble standard screwdrivers, the difference being that they have Torx or hex-shaped ends.

The handles usually have a hexagonal-shaped cross section that goes down the full length of the wrench. Allen screwdriver sets are ideal for cooperating with disc brakes and certain levers. The most popular size of Allen screwdrivers are ones measuring 1.5 millimeters to 5 millimeters.

Ball Hex Tools

Ball hexes are used to turn screws and bolts with hexagon-shaped socket heads. These have ball-shaped heads with tighter sides, making it simpler to slide keys into the desired slot.

The ball ends also let the user reach an offset 30-degree angle, letting them get to the required position quickly and efficiently. Ball hex tools are perfect for reaching tight areas that L-shaped wrenches cannot handle.

Adjustable Allen Wrenches

These wrenches have a mobile jaw that can change the wrench’s size, as well as a stable jaw area on top called a network wrench. Adjustable Allen wrenches can be bought in three different sizes, 200, 300, and 250 millimeters.

The wrenches are great for tightening or loosening screws or angled nuts. They can also be used for plumbing, self-assembly, car repair, and electric tasks.


Combination Allen wrenches are double-ended tools. One end has a box end, while the other end is open. Box-end Allen wrenches have closing rings in different diameters, depending on their size. Combination Allen wrenches are multi-purpose instruments.

The open end can tighten and loosen nuts and bolts inside small areas, but the box end delivers a tight grip on the fasteners. You can find combination Allen wrenches in bicycle repair shops.


These wrenches are made to access narrower areas that bigger or larger wrenches might struggle with. Open-end wrenches are made with openings of different measurements to fit the desired bolts or nuts. These tools have U-shaped openings at both ends that deliver a tight grip on items.


These Allen wrenches have a hollow cylindrical form that is fastened to the end of the handle. This is fastened to the bolts to tighten them or loosen them. Socket wrenches are thought to be an important tool and can be used on many different-sized objects.

As they deliver impressive speed and efficiency, they are ideal for many tasks and angles. You might hear some refer to socket wrenches as ratchet wrenches.


These tools are like open-end or box-end wrenches, except crowfoot wrenches, don’t have handles. They also have openings along the wrench’s rear face. These tools can slide into the side of nuts and bolts, and are particularly useful in tighter areas.

Crowfoot can be used for many fittings, like power steering, a few abs modulators, power steering, clutches, and brakes.

Standard Allen Wrench Sizes

Allen wrenches come in inch-based sizes and metric sizes. Here is a breakdown of the metric size and inch size of wrenches that match each other.

Inch Sizes and Metric Size Pairings

  • ⅛ inches – 2.5 millimeters
  • 3/32 inches – 3 millimeters
  • 7/64 inches – 4 millimeters
  • 5/32 inches – 5 millimeters
  • 3/16 inches – 6 millimeters
  • ¼ inches – 8 millimeters
  • 7/32 inches – 10 millimeters

Pros & Cons of Allen Wrenches


  • Easy to produce and are usually an economical choice
  • Lever arch component delivers better and tighter torque
  • Key doesn’t slip so it won’t injure the area surrounding the screw
  • Help prevent fasteners from separating
  • Used with hexagon-shaped fasteners which hold better than wrenches and screwdrivers
  • Powerful gripping motion prevents fasteners from snagging with removal or installation tasks


  • If a lot of pressure is applied to the sides, this can lead to the wrench wearing down
  • If the wrench is used frequently, the tip may break. You can avoid this occurring by examining the tips regularly

Final Thoughts

Allen wrenches are common tools used to turn screws and bolts. They have a beginner-friendly design and are relatively affordable to purchase.

They come in several different types that have different benefits depending on which one you choose, like the adjustable, socket, and combination style wrenches.


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