Allen Key Sizes Chart (2024)

Fasteners are available in different types, sizes, and metals. Fasteners with a hexagonal-shaped recess in the heads of the fastener are among the most useful.

These fasteners are referred to as hexagonal socket head screws or Allen screws, after the inventor. The fasteners are meant to be placed and removed with the aid of a specialized tool referred to as an Allen wrench or Allen key.

Allen wrenches are one of the most popular and frequently used tools in the toolkit of the average do-it-yourselfer. Their L-shaped heads easily identify them.

They are used for various applications, but mostly in vehicle repair, unclogging garbage disposals in sinks, and assembling prefabricated furniture.

Allen wrenches are frequently relatively small and are available in various standard SAE International sizes, including 5/32-inch, 3/32-inch, 7/16-inch, 3/16-inch, 1/18-inch, and 14-inch.

In our guide, you can learn more about how to use our Allen head size chart. By the end, you’ll no longer be stuck on determining Allen wrench size for the screw, as you can see how to measure Allen wrench size, so you pick the correct one. (Read Sockets Sizes in Order)

How Do I Know My Allen Key Size?

The Allen wrench comes from the mid-1900s and has become the standard for what we know as a hex key. The Allen Manufacturing Company is a registered trademark and created a set of quality hexagonal wrenches, which are standard and metric sizes, where Allen key sizes in mm are common.

Here you can find the only hex key size chart and the Allen wrench size guide you’ll ever need. The hex wrench sizes chart cover metric, and the Allen key size chart metric, and an Allen wrench chart where the Allen keys are made from another material and have the ball head.

Allen Keys Metric

Hex sizeLong arm lengthShort arm length
1.5 mm90 mm14 mm
2 mm112 mm19 mm
2.5 mm101 mm16 mm
3 mm123 mm21 mm
4 mm137 mm24 mm
5 mm154 mm27 mm
6 mm172 mm31 mm
8 mm195 mm37 mm
10 mm224 mm42 mm

Allen Keys Common Imperial Sizes

Hex sizeLong arm lengthShort arm length
3/32 inch112 mm19 mm
7/64 inch119 mm20 mm
1/8 inch123 mm21 mm
9/64 inch130 mm22 mm
5/32 inch137 mm24 mm
3/16 inch154 mm27 mm
1/4 inch185 mm34 mm
5/16 inch195 mm37 mm
3/8 inch224 mm42 mm

Allen Keys Common SAE Sizes – Imperial Alternative Material and Ball End

Hex sizeLong arm lengthShort arm length
0.05 inch83 mm14 mm
1/16 inch91 mm15 mm
5/64 inch100 mm16 mm
3/32 inch112 mm18 mm
7/64 inch119 mm19 mm
1/8 inch126 mm20 mm
9/64 inch132 mm23 mm
5/32 inch140 mm25 mm
3/16 inch160 mm25 mm
7/32 inch180 mm27 mm
1/4 inch190 mm34 mm
5/16 inch200 mm36 mm
1/2 inch224 mm40 mm

Which Size Do I Use

Allen screws are not pre-stamped on the top or side of the screw with the Allen wrench size needed and can add to the difficulty of locating the correct Allen wrench.

If you are uncertain, make a guess, and to minimize time wasted, you can start with the middle wrench in Allen wrench set sizes you have and work up or down the sizes until you find the right one.

The Allen wrench sizes are stamped on the side of the tool. The inch or millimeter size could wear, and it is here where an Allen wrench or hex key chart can significantly simplify determining the correct size for your socket head. (Read Star Bits Sizes Chart)

Most manufacturers include an Allen key size chart with their products.

An Allen key size chart is frequently included with self-assembled furniture, such as infant cribs, outdoor swings, or computer tables.

Hold onto your Allen key size chart in mm or metric, as using the wrong size Allen key on your hex bolt could easily strip the inside.
It is the manufacturer’s guide where you can learn how to measure Allen key size when the writing has gone. How to measure an Allen wrench is as easy as holding your hexagon Allen key or socket screw head against the diagram or image to determine the Allen wrench size.

What Size is a 4mm Allen Key?

Here you can find the best SAE Allen wrench for a given metric size. Metric to SAE hex wrenches don’t always have a perfect opposite, so you’ll need a separate metric hex key set, which is recommended as more hardware is produced internationally.

SAE and metric hex key sets can live together in your tool kit.

Last, having SAE & metric hex keys in the United States, you’ll find larger metric half sizes of sockets like 3.5 mm aren’t standard. However, a 9/64 Allen wrench in mm as an SAE hex wrench works in place of the 3.5 mm wrench. A 3/32 Allen wrench in mm, by comparison, would be 2mm.

Here, you can find the different sizes of the socket wrench and how it converts from metric to SAE. Between the two, you’ll find the right sizes Allen key for your screw.

Metric Hex Key SAE Hex Size

Metric Hex KeySAE Hex Size
2 mm3/32
2.5 mm7/64
3 mm1/8
3.5 mm9/64
4 mm5/32
5.5 mm7/32
6 mm1/4
7 mm9/32
8 mm5/16
9 mm3/8

What is the Most Common Allen Key Size?

In standard measurements, the most common Allen wrench sizes and bolts for common tasks are 5/32-inch, 3/16-inch, and ¼-inch sizes.

What Size is a T40 Allen key?

A T40 would be 9/32″ or 7mm.

Metric Sizes or Standard Sizes?

Using your Allen wrenches can dictate if the sizes are standard or in Metric. The right size, for instance, could be a metric if you have a foreign car.

Types of Allen Wrenches

Allen wrenches or Allen keys are available in different styles. The most common is the L-shaped hex key, yet you have variations incorporating different handle designs, different materials, or special features.

T-shaped Allen keys – T style Allen wrenches differ from traditional Allen wrenches in that they have a handle created from a wrench in the metal stock that leads to a single drive key centered across the handle’s width.

It enables a more pleasant action when used repeatedly and allows for greater torque to be exerted than with the traditional L-shaped Allen key, which is also available. Short and long lengths are also offered, so you can insert the shorter tools into tighter spaces or corners where a longer tool wouldn’t fit in the bolt.

Ball-end Allen keys – The ball head Allen key is one of the more distinctive types of Allen Key available. They are distinguished by the presence of a hexagon-shaped ball at the driving end of the tool. Allen wrenches of this sort are available in two different types: L-shaped and T-shaped designs.

Unlike traditional straight profiles, the ball end design on the driver allows for the tightening or loosening of fasteners when the tool is held at an angle concerning the fastener, which is not possible with the straight profile.

This is particularly useful in situations where the working clearances are such that a head-on usage of the tool is impossible or where a direct engagement would not provide enough room for the tool to rotate to apply torque to the application. (Read LightSocket Sizes Chart)

In general, these wrenches are not advised for high torque situations since the engagement with the fastener when the ball end is used is diminished when using this form of the wrench.

Excessive torque might cause the material of the hex surfaces of the socket to become stripped or the inserted ball of the wrench to come loose. Long and short lengths are also available in a variety of colors.

Some ball-end Allen keys have a ball at one end of the driver and a shorter driver extending off the handle with a regular hex head at the other end of the driver. Others may choose to use a ball at both ends of the tool or a single driver with a handle on one end of it.

Allen Key Sizes Chart (2024)


How do I know my Allen key size? ›

Most Allen wrenches have the size stamped clearly on the side of the tiny, angled tool. The inch or millimeter size may have rubbed off with use or may be entirely too small to read. In this case, an Allen wrench or hex key chart can make finding the right size for your socket head much easier.

How many types of Allen keys are there? ›

The three most common types of hex keys are L handle, T handle, and fold-up sets. The three common types of hex keys are L shaped, T shaped, and fold-up sets. The long arm on L shaped handles produces more leverage than the other hex wrench variants, allowing for higher torque and better reach into tight areas.

What is the difference between an Allen key and a hex key? ›

A hex bit is a hexagon-shaped bit that is designed to fit into a manual or power screwdriver or drill. An Allen wrench, in its turn, is a separate manual tool. However, both a hex bit and an Allen wrench have the same hexagon shape (if to look at the front side).

Is hex key same as Allen key? ›

A hex key, also known as an Allen key is a simple tool used to drive bolts and screws with hexagonal sockets in their heads. From standard keys in chrome vanadium steel to extra-long with ballpoint heads in chrome molybdenum steel, there are a wide variety to choose from.

How many sizes of Allen keys are there? ›

In addition to the precision sizes mentioned above, the common metric Allen wrench sizes are 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. Of these sizes, some of the more popular ones are 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, & 10 mm.

What size is M8 Allen key? ›

Metric Allen Key Table
Socket Shoulder ScrewKey Size
8 (M6)4mm
10 (M8)5mm
12 (M10)6mm
16 (M12)8mm
3 more rows

What is the most common allen key size for furniture? ›

The most common size Allen wrench used for IKEA furniture is the 4 mm, both the L- and S-shaped hex keys.

What is the largest size Allen key? ›

Millimeter wrench keys:

Most general purpose allen keys come in sets with sizes starting at 1.5mm up to 10mm. However we can find larger size wrenches with sizes 19-22mm which are also used frequently.

What are the two types of Allen keys? ›

Following are the types of Allen wrenches: L-style allen wrench. T-handle allen wrench.

What is the smallest Allen key size? ›

Allen wrenches can be measured in both millimeters or in standard sizes, which uses inches. Small specialty Allen wrenches can be as tiny as 2mm, or sizes larger than 25mm.

What size is M2 Allen key? ›

Metric Socket-Head Cap Screws
Metric Clamp ScrewHex Wrench Size (mm)
6 more rows

What size is an M8 in hex? ›

HEX Bolt Dimensions - ISO 4014
d1d1b to 125e
15 more rows

What size is h7 hex? ›

【Size】1/4-inch drive socket, H7 (7mm) hex bit, 1.5-inch (38mm) total length.
Finish typePolished
3 more rows

How do you remove an Allen bolt without an Allen key? ›

Use a standard screwdriver that fits the groove you just made snugly. Turn the screw slowly being careful as the screw head is not as strong as it was before it was cut. Your screw should back out nicely without ruining the surface it's screwed into.

What does a hex key look like? ›

A hex key, also known as an Allen key or Allen wrench, is a small handheld tool that's used for for driving bolts and screws with a hexagonal socket. They are available in many different sizes, though they all have the same hexagonal-shaped tip.

Why do they call it an Allen key? ›

The “Allen screw” name for the socket head cap screw and “Allen key” for the wrench originate from the products of the Allen Manufacturing Company of Hartford, Connecticut. According to Bates, it is widely reported that the company trademarked the name “Allen wrench or key” for its range of hex wrenches in 1943.

What size is M8 Allen key? ›

Metric Allen Key Table
Socket Shoulder ScrewKey Size
8 (M6)4mm
10 (M8)5mm
12 (M10)6mm
16 (M12)8mm
3 more rows

How do you measure hex? ›

Measure the Hex Key

Hex keys measurements are done across-flats or AF. This simply means that they are measured from one flat side of the head to the one directly across from it. Thank goodness for this little bit of knowledge.

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