Home Tech A User’s Guide to the most common Allen Key Sizes

A User’s Guide to the most common Allen Key Sizes

A User's Guide to the most common Allen Key Sizes

Allen keys, also known as hexagon keys, are used to tighten and loosen bolts and screws with six sides. In most cases, Allen keys are bunched together on a ring so that the keys are kept in one place. Also known as hex keys, hex wrench, or Allen wrench, these tools were developed by Allen Manufacturing Company and thus the name.

In many small industrial units, such as toy manufacturers, musical instrument manufacturers, motorbike manufacturers, garage builders and automotive engine manufacturers, Allen wrenches are used for a variety of purposes. Usually, self-assembly kits contain these screws. They are widely used in furniture assembly.

Allen keys are available in different materials, such as silicon steel, stainless steel, alloy steel, beryllium copper, etc., and in different finishes like gunmetal, phosphate, chrome and blackened finishes.

Types of Allen keys

  • L-shaped Allen keys:  As the name suggests, L-shaped Allen keys are shaped like the letter ‘L’. Both ends of an L-shaped Allen key have the same size head and can be used in either direction. If you need more torque, choose one with a longer arm, whereas if you need to access fasteners in tight spaces and provide control, when necessary, go for a key with a shorter arm.
  • T-Handle: The T-handle Allen key has a T-shaped handle making it more ergonomic. This makes it easier to apply a large amount of torque on persistent fasteners. For easier access, T-shaped Allen keys come with a secondary Hex Key integrated into the handle. One of the most popular wrenches used by bike mechanics and in the motorsport is the T-handle wrench.
  • Straight: These Allen keys are intended to give better torque transfer and more in the mould of a screwdriver. They sit nicely in your hand and offer improved control and more comfort.
  • Folding Hex: You can neatly fold the Folding Hex Key Sets into a handle and store them in a tool pouch or box. These keys are convenient and ideal for on-the-go applications. The main advantage is that you can fold the keys in 180 degrees or more, making it easier to reach hard-to-reach fasteners or replace them more quickly.

The most common Allen Key Sets

Allen keys are available in a number of sizes, both in metric (mm) and imperial (inches) units. 

The metric Allen key sizes are found from 1.5 mm up to 10 mm. 

  • 1.5 mm
  • 2 mm
  • 2.5 mm
  • 3 mm
  • 4 mm
  • 4.5 mm
  • 5 mm
  • 5.5 mm
  • 6 mm
  • 7 mm
  • 8 mm
  • 9 mm
  • 10 mm

The most commonly used ones are 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm.

The imperial Allen key sizes are found from 1/16″ up to 3/8”.

  • 1/16″
  • 5/64″
  • 3/32″
  • 7/64″
  • 1/8″
  • 9/64″
  • 5/32″
  • 3/16″
  • 7/32″
  • 1/4″
  • 5/16“
  • 3/8″

The commonly used Imperial sizes are 1/8″, 3/32″, 7/64″, 5/32″, 3/16″, 1/4″, and 7/32″.

If you need an Allen key for a precision job like watch making or electronics, you could go for imperial sizes 0.028″, 0.035″, 0.05″ and metric sizes 0.7 mm, 0.9 mm, and 1.3 mm. 

The key to tackling any fastener, whether you’re a novice or an expert, is to keep an Allen key handy at all times. To purchase the right Allen keys for your application, visit our website and go through all the high-quality brands available.

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