Is a Hex Key the Same as An Allen Key?

What is Hex key?

A hex key (also known as Allen key and Allen wrench) is a simple driver for screws or bolts that have a hexagonal recess, as opposed to the typical Phillips or flathead versions more commonly seen.

Hex keys are formed from a single piece of hard steel hexagonal rod having blunt ends that fit snugly into similarly-shaped screw sockets. The rods are bent to 90o, forming two arms of unequal length resembling an “L”.

The tool is usually held and twisted by its long arm, creating a relatively large torque at the tip of the short arm; it can also be held by its short arm to access screws in difficult-to-reach locations and to turn screws faster at the expense of torque.

Hex keys are designated with a socket size and are manufactured with tight tolerances. As such, they are commonly sold in kits that include a variety of sizes. Key length typically increases with size, but not necessarily proportionally so.

Variants on this design have the short end inserted in a transverse handle, which may contain multiple keys of varying sizes that can be folded into the handle when not in use.

Why are they called “hex keys”?

These instruments are essentially L-shaped wrenches that have six sides. They are utilized to drive hexagon-shaped recessed holes. Greek “hex” means “six”. Hence the name.

Why are they referred to as “Allen wrenches”?

At the beginning of the 20th century, William G. Allen patented a cold drawing process for making hex socket set screws. Wrenches to turn these screws would make Allen famous. “Allen” is a registered trademark, however, even wrenches from other manufacturers are sometimes called Allen wrenches.

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Features of Hex Keys

Some features of hex keys are:

  • The tool is simple, small and light.
  • The contact surfaces of the screw or bolt are protected from external damage.
  • There are six contact surfaces between bolt and driver.
  • Very small bolt heads can be accommodated.
  • The tool allows the use of headless and recessed-head screws.
  • The screw can be held by the key while it is inserted into its hole.
  • The torque applied to the screw is constrained by the length and thickness of the key.
  • The tool is cheap to manufacture, so it can be included with products requiring end-user assembly.
  • Either end of the tool can be used to take advantage of reach or torque.
  • The tool can be reconditioned by grinding the worn-out end.


Different Types of Hex Keys:

  • L-Style Allen Wrenches.
  • T-Handle.
  • P-Handle.
  • Folding Hex Key.
  • Ratcheting Drivers.
  • Torque Wrench.
  • Allen Screwdriver.
  • Ball Hex Sets.
  • Key Ring Sets.

1. L-Style Allen Wrenches

This is the standard Allen key and is easily found anywhere. Due to its L-shape, it can reach into tight spots and provide control when needed. If you are looking to get only one set, this would be a perfect option. There are many choices available in the market, though a 1.5-10mm is a good value purchase.

2. T-Handle

This is a popular tool, mostly used in motorsport applications. Due to the T-handle, you can spin the wrench quickly, while allowing enough leverage in common usage. Beta 951 wrenches allow it to slide into a position to create an L-shaped tool. These are quickly becoming popular among bike mechanics.

3. P-Handle

These types of Allen keys can be seen in lots of professional workshops. These are oversized L-wrench with a comfortable grip that gives them similar benefits as a T-handle.

4. Folding Hex Key

These are mostly loved by bicyclists and motorbike riders. Unlike other Allen keys, it is nearly impossible to lose a folding Hex wrench, as they are enclosed in the handle. They are normally folded out at 90 degrees from the storage handle to give maximum torque.

5. Ratcheting Drivers

Ratcheting Hex drivers provide better speed in comparison to the traditional Allen wrenches. These tools are more dynamic, as they are used with screwdriver bits and even sockets. They are available in different varieties. The bits of Ratcheting Hex Drivers can be used in an electric drill driver. It is a popular choice among people working with rotor bolts.

6. Torque Wrench

A torque wrench is an important part of any workshop, especially when working with delicate components. But it is definitely not a replacement for Hex wrench.

7. Allen Screwdriver

This is very handy when low torque and tight clearance are the main factors on which you are working. This is best for adjusting lever and some disc brake levers. The most common size used in the market is 1.5-5mm.

8. Ball Hex Sets

These wrench sets are distinctive from other Hex sets available in the market. They have ball molded heads at tight edges, where L-formed wrenches can’t exactly reach.

9. Key Ring Sets

These are basic L-shaped Hex or Toque keys mounted on a key ring with a spring retaining clip. These key sets are very affordable and can be kept in a house or car for convenience. To use the long arm, you have to twist and pull the key from the retaining clip. To replace it, you need to push and twist the key.

Five Uses for Allen Keys

Here are 5 uses for Hex key that will change the way you build, repair, and maintain in the workshops.

  • Bicycle repair. These are the dominant tools used for bike repairs and size adjustments. The wide range of sizes allows them to be used in different applications, and their compact size makes them easy to carry. If you are a frequent rider, you can pick a set of folding hex keys.
  • Furniture repairs. Allen screws are an essential piece of hardware for securing furniture at its place. It allows assembling the furniture without adding any unnecessary bulk pieces. Their compact design makes them discrete in appearance and strong in fastening. Since furniture pieces can have tight spaces and require long reach, you can use a set of long arm Hex keys.
  • Cars and motorcycles. You would need an Allen key set for the proper maintenance of your car. Allen keys are helpful while accessing the areas under the seat, and places under the dash like behind the glove compartment. T-handle Hex wrenches are recommended for cars and motorcycles repair.
  • Tools. Apart from other uses, Allen keys can also be helpful in maintaining and repairing heavy tools and machinery. Drill bits rely on it to secure the bit into place. Similarly, power saws of all varieties require Allen keys to change blades or for minor adjustments. Short arm Allen keys are mostly used to perform these tasks.
  • Electronics. Allen wrenches are becoming very popular with people dealing with repairing and maintaining electronics. As electronics are becoming more and more compact in size, Allen keys are being used to support their size. Computers and large television screens are held together with these screws from the backside. You can buy torque wrenches for this purpose. They are the main items in every electrician’s toolbox.

How To Get A Rounded Allen Key Bolt Out?

The problem usually comes from rounding out the hex head with the Allen wrench. It always seems like the wrenches are just not tight enough. If you don’t know how to deal with this, a small job can turn into a huge headache!  Here are some tips to help you prevent the problem in the first place and on how to deal with it, should it happen.

Prevention: Here is a list of things you should do to prevent rounding out a hex head bolt

  • Always thoroughly clean down inside the hex head hole. Use a pick or small screw driver to clean out debris.
  • The wrench must fit tightly all the way down into the head of the bolt. Don’t use worn wrenches
  • Try to HIT the head of the bolt with a hammer and punch before attempting removal
  • This shock treatment helps to slightly loosen the grip of the bolt head to the surface
  • Don’t use a slow turning motion with the wrench. This can actually increase the chance of rounding out the head.
  • Rather, use a quick snap or jerk of the wrench to break the bolt loose

Cure:  If it still happens here are some options for bolt removal

  • If the damaged bolt is out in the open try grabbing the head with a pair of vise grips to loosen it.
  • As an alternative use a sharp chisel and hammer. Catch the edge of the head with chisel and hammer the head counter clockwise.
  • Use torx or star bits. This has become my favorite method. You may have to grind or modify the tip to get it to fit tight. See notes below:
  • If all else fails you will have to drill the head of the bolt off. Rent a right-angle drill if space is limited.
  • Motor mount bolts (particularly 116, 123 and 126 chassis) – you cannot get to the heads on some of these as they are up inside a hole in the subframe. If you cannot get them out with a star socket or oversize hex then you will have to drill the head off and find a good used replacement motor mount arm.

I always have a set of Torx bits in my toolbox of hex head bolt troubles.  You need to find a Torx bit slightly larger than the bolt head size. Then you can drive the bit into the head of the bolt with a hammer for a super tight fit.

This may require that you modify the Torx bit on a grinder. You can grind the sides off slightly or as in the picture below, you can grind off the tip to get the bit to fit tightly in the damaged bolt head.  This really works.

How To Remove Stripped Recessed Allen Bolt?

A flat sunk bolt with Allan’s head was torn out, the hex key had no grip and the sunk bolt could not be grasped with pliers. It was a fat bolt so drilling out would have been very difficult.

To remove stripped counter-sunk Allen-key bolts

Cut a slot into the screw head. Place a screwdriver in the slot and tap with a hammer in the counter-clockwise sense to loosen the bolt. Unscrew the bolt with the driver.

Use the same technique for Philips or crosshead screws.

Use a grinding/cutting disk, not a saw blade. Apply the rotating cutting disk gently, do not force or it will break. If this is a toughened steel or stainless-steel bolt (much tougher), it will be best to use a reinforced cutting disk. Use a dusk mask to avoid breathing the dusk from the disk!