Cool Tool Tuesday #2: Your complete guide to hex keys

Apr 30, 2023

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There are a number of indisputable truths in this world. Beer is better cold. There is never an OK time to wear worn-out lycra. And the vast majority of fasteners found on modern and quality bicycles feature a six-sided metric interface, designed to be driven with a hex key of a suitable size.

The humble metric hex key (aka Allen wrench) is without question the cornerstone to building, fixing, adjusting, or just maintaining a modern bike. And because of this, it's the hex key that I’ve obsessed about more than any other tool.

In this second edition of Cool Tool Tuesday, I aim to explain how professional mechanics gain efficiencies by using multiple styles of hex keys, what those hex key styles are, and what I choose to use. This is a long one but I expect that what's covered here will be referenced plenty in the future, so I figured I’d best cover it sooner rather than later.

As with most tool selections, hex key choice can be hugely personal and subjective. Many home mechanics will likely find themselves more efficient by sticking with a single set of hex keys that they’re comfortable using, while a full-time mechanic may find it more efficient to have easy access to 10 different types of a 4 mm (guilty).

And in case you’re wondering why I’m calling them hex keys and not Allen wrenches, well, that's because Allen wrench (part of the original Allen Manufacturing Company) is a brand trademark that has become somewhat of a generic term. It's a hex key, a hex tool, a hex bit, a hex wrench.

And what about Torx, the close relative and the star of the family? You’ll be pleased to know that just about everything mentioned in this article is also applicable to Torx tools, and yep, that includes the limitations of ball-end tools, the handle shapes, and my attack on three-ways (aka Y wrench).

When it comes to working on bicycles, I consider a regular set of hex keys to be one that covers the range from 1.5 to 10 mm (or more specifically 1.5, 2, 2.5, 3, 4, 5, 6, 8 and 10 mm). In rare circumstances, you’ll find uses for smaller and large sizes (or those outdated SAE sizes), but the above will service the vast majority of modern and not-so-modern bicycles.

It's also worth stating that having one full set that covers the common size spectrum means you probably don't need to buy full sets of other hex key styles that intrigue you. For example, I have a heap of 4, 5 and 6 mm hex tools in all shapes and sizes because it is what most bikes feature, while relatively speaking, I have fewer tools in the other hex drive sizes.

Before I dive into the various types of hex keys, let me first cover a few common (and not so common) features of hex keys to know.

Imagine a bicycle wheel that sits loosely in the dropout. As you ride it, it rocks back and forth and abrades away at the frame dropout until the two no longer fit together properly. It's the same story with using a loose-fitting hex key: pretty soon, the fastener will become worn or damaged and need replacement. Quality hex tools tend to fit fasteners better, and the result is a tool that can save both money and time.

A hex tool should measure as close to its quoted size (e.g. 5 mm across the flats for a 5 mm size) without going over that number, or at least that's the case in an imaginary world where all fasteners are perfectly matched to specification where the socket width measures a hair over its intended size (e.g. a 5 mm socket head cap screw would have a tolerance of between 5.020 – 5.084 mm, as outlined by the American National Standards).

Unfortunately, it's common to come across fasteners that are either oversized or undersized to the standard, and the latter case means a tool that's too close to its quoted size simply won't fit. Because of this, it's normal for most quality hex keys to be slightly undersized to ensure widespread compatibility.

To test the fit, you can simply put the tool into a fastener. The more rock or wiggle the tool has, the more likely damage to the fastener will occur. It's not uncommon for me to reach for a tool that I know is larger in size in order to better fit a loose-fitting fastener.

However, the size of the hex is not the only thing that will determine a good, reliable fit. Tool geometry and even surface finish can play a role in how securely the hex tool fits.

Most tools offer a chamfer on the edge for easy placement into the fastener. Meanwhile, some focus on sharp edges to make the tool hold tight, while others, such as Wera's HexPlus design, almost go the opposite way of rounding the edges in an effort to increase contact surface area with the fastener. In my experience, no one feature automatically makes a tool superior.

The hex tool size is related closely to the torque required. The greater the holding force required of a fastener, the bigger that fastener should be. And in turn, the bigger the tool interface should be to handle that higher load.

It's for this reason that a set of hex keys scales with the increasing tool sizes. And equally, the bigger the hex key size, the greater the leverage you’ll need to achieve (or undo) the matching torque requirement.

When it comes to gaining leverage in a tool, it's often as simple as having a longer lever. The longer the lever, the more force produced for a given effort. It's a game of simple mechanical advantage.

I’m personally a fan of having tools with more leverage than what you may commonly require. Occasionally you’ll come across a stuck fastener which the extra leverage will quickly overcome, and at other times, you’ll just be using less effort.

However, do be warned that in the wrong hands, a longer lever can make it easier to over-torque and strip bolts. If you’re unsure how much torque is too much, then you need a torque wrench.

As hex tools go up in size, they also tend to increase in diameter and length. This means that hex tools for smaller fasteners are more flexible versus those designed for larger fasteners. Experienced hands can use this flex to get a good feel for the torque of a bolt.

This flex is just one reason why I prefer L-shape hex keys with a consistent extruded shape for the whole length versus tools with a larger diameter rounded centre section.

A regular hex tool is designed to be used in a straight plane to the fastener. A ball-end allows the hex tool to be used at angle which greatly opens up access in tight confines.

A ball-end works by rounding the tool end and therefore reduces the surface area of the tool with the fastener. As a result ball-ends are typically unsuitable for high torque applications such as initial loosening or final tightening. For this reason most hex keys will put the ball-end in a position where it's difficult to apply lots of torque.

Often the ball-ends on lower-cost hex keys are susceptible to breaking and easily stripping out fasteners. More expensive offerings are typically more useful and are capable of applying torque at steeper angles.

A holding feature is there to aid with holding a loose fastener to the tool. This feature usually comes in the form of a small sprung ball bearing, a captive O-ring, or similar. Tools with holding features are typically less durable than those without.

Designed as a free-spinning grip that lets you quickly twirl the tool, spinners are often found on more premium T-handle and P-handle hex keys. Realistically, a light grip on the tool achieves the same thing as a spinner, but it's a feature that many still like to have.

I personally find short-length spinners that only take up a small amount of the tool's exposed length to be fine. Meanwhile, spinners that cover the full length of the tool can be a hindrance to feeling when the initial part of a thread has been located correctly.

For when a fastener head is stripped out, a twisted end or similar is designed to bite into the hex socket and allow removal of the fastener where a regular hex key has failed. This is a relatively new feature that you’ll find on Clever Standard's T-handle hex keys, Park Tool's sliding T-handle hex keys (see above photo), and a few others. I’ve honestly found it to be quite hit-and-miss, and I often have just as much success using a tight-fitting hex key (or hammering a Torx bit into place).

While it may occasionally prove nice to have, I personally wouldn't recommend buying a tool based only on it offering this feature.

There are a number of brands now offering colour-coded tools for easy size identification. It's a simple life hack that works.

It was my original set of PB Swiss Rainbow hex keys (the first company to do colour-coded hex keys) that got me on this more efficient path. Since then I’ve taken to matching many of my other hex tools with pieces of matching colour heat shrink or electrical tape. I personally keep it quite simple and only mark my 4 mm, 5 mm, and sometimes 6 mm heys.

In theory, you can pick whatever colours suit you, but in reality, you should copy the guidance that has fallen upon us from the Swiss mountains. The 4 mm should be yellow. The 5 mm should be orange. And the 6 mm should be red. You can butcher this rule if you please, but also, please don't.

As is often the case with tools, you often do get what you pay for. Without getting into the science of metallurgy, spending more on hex keys typically results in a tool with a better fit in the fastener, greater durability, improved corrosion resistance, and higher strength. You also get access to some of the more premium features covered above.

And then there are less obvious elements, such as improved warranty and the ability to buy one-off replacements if you happen to lose or wear out your favourite size. And sometimes a more expensive tool simply gives a ‘feeling’ one can't describe.

I’m a big proponent of buying quality tools that last versus buying junk that could damage your bike before the tool itself disintegrates. Hex keys provide a tangible example of just this and are certainly likely to get used enough to justify the additional upfront expense.

Below is a list of the most commonly and uncommonly found hex key types, in no particular order. In most cases, the name is based on the shape of the tool.

The ubiquitous hex key. Your old IKEA furniture most certainly came with one of these, and you most likely have a set of L hex keys already.

The L hex key is a staple and I strongly believe it's the style every mechanic or DIYer should own first. That's because while it may not always be the most ergonomic or fastest option, it’ll almost always fit the fastener you need to access. Even if you find an alternative style of hex key you prefer, it's always a good idea to keep a full set of regular L-wrenches at easy access for when tight clearance situations demand it.

I personally use long-length ball-end hex keys as I find these offer the best combination of comfort, usefulness, and speed.

Best on a budget: Bondhus Bright Guard, Extra Long, Ball-End (Part #17099, pictured bottom right in the image above). What I use: PB Swiss 212-LH Rainbow (also consider Wera and Wiha)

Incredibly popular in motorcycle mechanics, T-handles offer a long reach to the bolt with a comfortable grip on top. The grip doubles as a balanced weight to allow easy and fast spinning of the fastener.

A classic T-handle is designed to flex at the appropriate torque for the bolt head size and therefore offers an experienced mechanic a certain amount of torque feedback.

While not always the case, most traditional T-handles only feature a hex drive at the end of its long shank and are therefore not ideal for high torque applications where leverage is required.

This style of tool is ideal for when there's unimpeded straight access to fasteners, such as stem bolts. If buying this style of tool, I’d suggest not bothering with anything bigger than a 6 mm.

Best on a budget: Bondhus ProGuard or Eklind 55166What I use: I don't use this style of tool. Instead, I prefer to use P-handle, sliding T-handle, and Cross Handle wrenches, which closely overlap in purpose.

While most traditional T-handles only offer one tool end, Sliding T wrenches add tool ends to both sides of the handle. In doing so, the sliding T-handle is still designed to work much like a regular T-handle, but then the handle can also be slid to allow the tool to be used like a L wrench.

In some cases, the head and handle of the sliding T-handle function can cause clearance issues, which means it's not a guaranteed replacement for the humble L key. Similarly, the stiffer design of this tool style means it lacks the torque feedback of more traditional hex keys.

I’ll have a detailed comparison of the best and worst sliding T-handles soon. Yeah, I’m a tease like that.

Best on a budget: TBC.What I use: TBC.

Thanks to the likes of Park Tool, Pedro's, and Unior, this style of hex key is perhaps the most commonly used in bicycle workshops around the world.

The P-handle hex key is effectively an L key where both ends are lengthened and then an ergonomic grip covers the bend.

The long blade provides good reach and plenty of leverage. Meanwhile, the comfortable handle can be used when driving either end of the tool. I find this style of tool most useful in the 3-10 mm range. Otherwise, I find sizes smaller than that to be cumbersome and often overkill for the purpose.

It's also important to know that the handle will occasionally get in the way if clearance is tight, such as with certain seatpost designs or disc brake caliper bolts.

Best on a budget: Pedro's and Park Tool are both great and represent good value for the quality provided.What I use: Wera 454 HexPlus (no ball-end) and PB Swiss 1208 (available with a ball-end). Although I’m equally happy using Park Tool and Pedro's options.

Pedro's and Park Tool (and likely others) offer tools specifically designed for tight pedals and crank bolts. These tools, typically only available in 6, 8 and 10 mm sizes, are effectively just massive L wrenches with a comfortable grip given at the longest leverage point.

Best on a budget: Pedro's and Park Tool are reliable options. What I use: While these tools can be useful to own, I find that a quality set of long P or sliding T-handles is just as good. I move to a breaker bar/sockets (see lower down) if further leverage is required.

This style of tool is effectively a shrunk down T-handle or a P-handle with only a hex tool at the end of the long blade. It's most commonly used for smaller fasteners, including precision work.

You use this style of hex tool much like a regular screwdriver, but the flat handle allows you to apply more torque. I find them quite comfortable and handy for tasks such as disc brake caliper adjustments where your hand can be quite close to the spokes. This style of tool is commonly only found amongst a handful of specialist tool manufacturers outside of cycling brands.

Best on a budget: This style of tool is often only offered by premium brands and is more common in Torx drive. What I use: PB Swiss 207 L (in 4 and 5 mm sizes only).

The three-way, also known as the Y-wrench, is a classic cycling tool that puts three common hex tool sizes into the palm of your hand. They’re so common that just about every cycling tool brand offers one.

Personally, I think these tools aren't nearly as useful as they once were. Modern bikes seem to now have fasteners in more awkward spots that commonly prevent the easy spinning of one of these tools.

For example, the shorter stems on modern mountain bikes don't provide enough room to spin a Y-wrench without the other tools hitting the handlebar, while many three-ways also aren't long enough to clear the out-front computer mounts found on many road handlebars if you need to access the faceplate bolts. And then don't even bother trying to use one of these on integrated seatpost binders or dual-bolt seatpost clamps.

Best on a budget: Park Tool (avoid the ball-end version because it's silly).What I use: I honestly used to love spinning these, but now I only use the one that's kept in my car for removing bolt-up thru-axles.

This is Abbey Bike Tool's answer to the Three-Way, and as the name suggests, it adds a fourth tool.

I initially hated the shape of this tool and found it pokey in the hand, However, I grew to like it more once I stopped trying to hold it like a three-way.

I find this tool useful on tasks where a screwdriver is great but sometimes you want more leverage. In this way, it's much like the flag driver covered above. And of course, it's also great on smaller hex fasteners where it can be difficult to see whether you need a 2 or 2.5 mm hex until you’re at the fastener and can see what fits.

I like this tool, but it's far from a must-have. It can be quite uncomfortable in the hand if you’re trying to apply a lot of torque. And the shape is prone to clearance issues, such as getting into certain sunken derailleur bolts or turning the fasteners of most seatpost designs.

Best on a budget: There is only one option – Abbey Bike Tools. At US$40, it's not cheap (but also it's made in the USA and uses hex bits from Wera). What I use: I have a few of these, but what I use most features 2, 2.5, 3, and 4 mm hex bits.

Is it a multi-tool or workshop tool?

This is the tool of choice of Dangerholm and a surprising number of mechanics around the world. In the right hands, the combination of the compact size and obvious flex give plenty of torque feedback, and there's the obvious argument that you always have the right size in your hand.

The folding shape means the tool can be quite modular in its use; the handle can add leverage and be flipped over and around obstacles that sit in the way. Meanwhile, the handle can be aligned inline to the tool and be used as a screwdriver handle.

Best on a budget: Bondhus or Park Tool. What I use: Nope, not me.

Imagine an L-shaped hex key where the head flips 180º to allow the tool to either be used as a screwdriver or to be swivelled around obstructions. OK, there's no need to imagine it; it exists.

To my knowledge, this design is only readily available from two companies, Bondhus and Motion Pro, and both offer identical tools. These tools have a small but loyal following among pro race mechanics and for good reason: with practice, they can be used extremely efficiently.

Best on a budget: Not much choice here and they can be fairly expensive. What I use: Yes, I have a set. No, I don't use them. I suspect I’d put them to use more often if the larger sizes offered both more leverage and more strength.

Yep, you can get hex tools with screwdriver handles. And yep, I’m a big fan. I get a heap of use out of my 2, 2.5, and 3 mm sizes, and while you may think there are better tools for adjusting newer-style derailleur limit screws or brake lever reach screws, you’d be wrong.

On my tool wall, I have a set of these from 1.5-5 mm. The 1.5-3 mm sizes have regular straight hex ends, while the 4 and 5 mm are ball-ends. I don't recommend using ball-ends for the smaller sizes because you’re just asking to strip the fastener heads (i.e. cam-out).

I use this style of tool for bottle cages, brake lever adjustments, derailleur fine-tuning, and anything else in that vein where leverage isn't commonly needed and a handle just gets in the way.

Best on a budget: Bondhus (but only available in ball-end). What I use: PB Swiss SwissGrip 8205 (I don't mean to sound like a PB Swiss fanboy, but these have a reliably tight fit in the fastener and the best ergonomic screwdriver handle going). I switch to ball-ends for the 4 and 5 mm sizes and don't own any bigger than that.

Ever come across a situation where the fastener has something directly above or next to it which stops you from getting your hex key in it? Examples include front derailleur braze-on bolts blocked by bidon cages, or poorly thought-out disc brake caliper mounting positions. This is where low-profile hex keys come in and there are a few different types.

The most common is the simple stubby L wrench, which merely offers a shorter short side versus a regular L key.

My preference is for offset stubby L wrenches that put the short side at an approximate 100º angle (seen on the yellow and orange keys above) instead of the usual 90º bend. This design optimises the space available.

Then there are dedicated low-profile hex tools that use special shortened 1/4" bits to fit into impossibly shallow spots. The slimmest of these have the bit bonded into a thin plate of metal, but there are low profile bit ratchets that aren't too much thicker.

Best on a budget: Bondhus Stubby ProGuard (Park Tool offers something closely comparable, too). What I use: PB Swiss 2212 or Vessel TD-76 bit ratchet.

As covered in episode #1 of Cool Tool Tuesday, a bit ratchet is a compact tool that can be a real time-saver. A bit ratchet merely works with common 1/4" hexagonal bits and lets you drive a fastener without having to constantly remove the tool and replace it at a different angle.

Best on a budget: PrestaCycle T-Handle and bits (also sold under a number of other brands for more money).What I use: PrestaCycle T-handle or the identical Facom I paid five times more for, with PB Swiss or Wera bits.

Another tool type covered in the previous episode, a square drive ratchet is designed to drive common automotive sockets. This style of ratchet is most commonly found in three drive sizes (1/4", 3/8", and 1/2"), with each size up intended to handle increasing torques.

I personally use 1/4″ square drive ratchets a great deal, and have a couple permanently set up with 4 and 5 mm hex bit sockets. I use a long-leverage 3/8" ratchet for driving 8 and 10 mm hex bit sockets (in addition to bottom bracket sockets and the like).

Best on a budget: Countless options, but it often pays to spend more to get one with reduced backdrag. If that's not a priority for you, then something such a GearWrench 120XP represents strong value for money. What I use: Nepros 90T and Snap-On THL72 with Nepros, Gedore and PB Swiss bit-sockets.

A bit holder tool uses the same common 1/4" hexagonal bits as a bit ratchet, except the tool handle doesn't ratchet. These tools can be handy for when you’re trying to save space or money by not buying whole hex keys sets with dedicated handles. They can also make for a compact multi-tool. I’m certainly a fan of bit-based multi-tools.

There are some great bit holder tools on the market that come in just about every shape and size covered above. You can even adapt a 5 mm hex key to be a bit holder with the right adapter (PB Swiss Part #470 M).

The main limitation of bit holder tools is that the bit holder itself always features a larger diameter than the hex bit you’re using, meaning clearance into sunken fasteners (such as some rear derailleur bolt designs) can be an issue. Similarly, some bit-holders feature weak magnets and so can commonly leave the bit stuck in the bolt which gets annoying quick.

Best on a budget: Countless options, although the Park Tool QTH-1 quick-change driver set deserves a special mention for its unique one-handed loading/unloading design. What I use: I just about never use this style of tool. If I’m using a bit-holder, it will have a ratcheting function.

For truly stuck pedals or crank bolts, I’ll often reach for a breaker bar. This is a simple tool that combines a long handle with a square drive socket holder at the end. It uses the same sockets as a square drive ratchet (but often in a larger drive size).

While rarely needed, truly stuck pedals or crank bolts are (almost) always defeated by my 24"-long breaker bar with a 1/2" drive. This is typically a last resort tool when my more common-length hex tools aren't getting the job done.

Best on a budget: It's a simple tool, so often the generic options sold by your local automotive care store will do the job (e.g. Harbor Freight for those in the USA, SuperCheapAuto for those in Australia).What I use: Beta (made by Koken) 24" length, 1/2" drive size.

Torque wrenches are a different category of tool than hex wrenches. Yes, torque wrenches are commonly fitted with hex bits to drive hex fasteners, but the purpose of a torque wrench is for accurate torque setting of a fastener and not for undoing or general non-consequential bolt twirling. Even if you own a torque wrench, you should still own a set of regular hex keys (or 10).

Best value: TBCWhat I use: Well, that's a whole different article …

So there you have it: more than you wanted to know about different types of hex keys.

Just remember that hex key choice is hugely personal and what you’re used to using is typically going to be the tool you favour most. What's your go-to?

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Note: A number of the tools mentioned in Cool Tool Tuesday are not sold through traditional cycling channels and can be hard to find, which is also kind of the point of the series. Access to the tools covered will be easy for those in Europe and the United States. Use a search engine to find the products mentioned.

This content is produced independently and purposefully without related advertising, affiliate links, or other commercial interests. Like much of our content, it is funded by VeloClub members. If you found this content valuable then please consider joining.

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