There are numerous useful sizes available of an Allen wrench. When you are in the middle of building something, the variety of sizes can be confusing.
You can choose the style of Allen wrench you need for a project using a few different methods. The screw’s diameter affects the size of the Allen wrench, allen key, or hex key needed.
In this article, we will discuss how you can discover what size Allen wrench you need for your project, and how to effectively use hex keys for all manner of socket screw head and metric sizes.
Allen Wrench History
The Allen wrench was first invented in the middle of the 20th century. It became the accepted term for what was before known as a hex key.
This is due to the company known as Allen Manufacturing having designed a line of high-quality hexagonal wrenches and quickly produced them.
In the same way that brand names like Kleenex and Band-Aid are frequently used in place of the common terms such as tissue and bandage.
Therefore, the previous hex key started to be referred to as an Allen wrench. Now both names are talking about the same tool
Allen Wrench Sizes
Allen wrenches are produced in various sizes. However, you can commonly find them in both metric and standard sizes.
Standard Size
The standard size of Allen wrenches are commonly measured in inches. The inch based set is seen as a standard in the tool industry.
In a standard size set of Allen wrenches you can see various different sizes including the following:
- ¼ inch,
- ⅛ inch,
- 3/16 inch,
- 3/32 inch,
- 5/32 inch,
- 7/32 inch,
- 7/64 inch.
Metric Size
The metric size of Allen wrenches are also sometimes referred to as the European standard size.
If you're interested in learning more about specific sizes and uses, visit our guide on Allen Wrench Sizes for detailed information.
These Allen wrenches are measured in millimeters (mm). Therefore, the sizes found in a metric/ European Allen wrench set includes the following:
- 2.5 mm,
- 3 mm,
- 4 mm,
- 5 mm,
- 6 mm,
- 8 mm,
- 10 mm.
Which Size Of Allen Wrench Should You Use?
Sadly, screws with divots do not have the particular size of Allen wrench they need stamped on them.
This makes it a little difficult to get the right-fitting Allen wrench straight away.
You will need to take an educated guess if you are absolutely unsure on which Allen wrench to use. The best thing to do is start in the middle of your Allen wrench set.
Then depending on how well that Allen wrench fitted, you can either move up or down in size until you find the Allen wrench that fits correctly.
Use A Allen Wrench Size Chart
The size of most Allen wrenches is clearly printed on the side of the small, angled tool. It’s possible that the inch or millimeter size has worn out over time or is simply too small to read.
Finding the correct size for your socket head can be made much simpler in this situation with the aid of a hex key or Allen wrench size chart.
An Allen key size chart will typically be published by the manufacturer of your sets.
A size chart for Allen screws is frequently included with furniture that you must assemble yourself, such as computer desks, outdoor swings, and infant cribs.
You should try to keep a hold of this document. Pin it up somewhere, so then you can hold up your Allen wrench up to the actual image.
This might assist you in determining the size of Allen key you require or need to have on hand.
Measure The Screw Hole
If you are still struggling to find the correct Allen wrench size for our screw, then you could always measure the size of the screw hole.
This will then give you a rough number to try and find within your Allen wrenches. You want to find a similar size of your screw hole to your Allen wrench set.
Although, with this method, it will involve you measuring all your Allen wrenches until you find one that is a close match.
Thus, it is time-consuming, but it is an accurate method to use if you have the time to do it.
Why Is It Important To Use The Right Size?
Although Allen keys look quite durable, they can harm a screw head if the incorrect size is used on it.
A hex screw or bolt can be easily stripped or the smaller Allen wrench can be stripped down, if the wrong sizes are used.
Ensure the bolt head is free of debris and dirt, before inserting the Allen key.
Any dirt or dust that might gather in the corners of the hexagon, can be removed with a wipe of a Q-tip soaked in rubbing alcohol.
Prior to starting to tighten or loosen a bolt, always make sure that both sides of your Allen key are correctly aligned into the hole.
If you don’t, you risk damaging the wrench or stripping the bolt’s head.
What Should You Do If You Don’t Have The Right Size That You Need?
There are a few options if your Allen wrench set doesn’t contain the size of Allen wrench you require.
This first tip will only work if you have an interchangeable screwdriver. This is a screwdriver where you can switch in and out different heads.
On some occasions, you may find that the head tips that are included with these interchangeable screwdrivers will include Allen wrench heads as well.
Thus, you may be able to find the size you need here.
The other option that you have consists of using a flathead screwdriver. Although, this option only works if your flathead screwdriver can slot into the corners of the hex screw or bolt.
If the screwdriver does fit, then you can attempt to turn the screw with the flathead screwdriver.
However, you need to make sure that the fit is extremely snug, so you don’t risk damaging the screw or your screwdriver.
Where Can You Purchase Allen Wrenches?
Most stores offer quality Allen wrench sets both in-person and online. Hardware retailers like Lowe’s and Home Depot are more likely to carry a variety of hex key sizes.
A fantastic alternative is a tool company like Bondhus. Still, the majority of the shops will sell regular sets. The range of sizes you require will determine where you should shop.
Look at the following stores to purchase Allen wrench sets:
- Amazon,
- Lowe’s
- Home Depot,
- Harbor Freight,
- Walmart.
Final Thoughts
Typically, when you are building something, such as a desk, it will come with the correct size Allen wrenches included.
However, if you are doing jobs around the house, you will need to discover what size you need.
To know what size you need it’s best to look at the size of the screw top’s head and through trial and error you will find the correct one that fits. Or you can try using an Allen wrench size chart.
We hope this article has been useful in helping you discover how to know which size Allen wrench you will need.
For more information on the history and differences between similar tools, check out our article on Allen Wrenches vs Torx Wrenches.