Bolt Tech – Will Torx Win?

All images © Greg Kopecky / slowtwitch.com




Don your geek hats and hold on, because we’re about to talk about the most exciting bike part - ever. This is the stuff that keeps me up at night… weighing the pros and cons, considering weight savings, hemming and hawing about longevity.

I don’t count sheep. I count bolts.

Bolts, you say? Yes – bolts. What could be so exciting about such a boring piece of metal? Well, without them, your bike would fall apart (or at least parts of your bike would fall apart). You should love and cherish your bolts.

The thing you may or may not realize, however, is that bicycle bolts are evolving. In the past decade or so, we’ve seen a slow influx of a relatively new bolt standard – Torx. Most of you are familiar with the venerable Allen, or “hex” bolts that your bike has. Bicycles typically use metric sizes ranging from 2mm to 10mm. They’re generally easy to work with, and look something like this:

You’ll find these on your seatpost clamp, stem, cranks, bottle cages, and just about anything that needs to be fastened together. What then, is this new Torx thing? And why is it out to kill my beloved Allen wrench?

Torx is a standard that debuted in the late 1960’s. It is distinguished by a 6-point star pattern that looks like this:

The reasoning behind this special design is to resist stripping the bolt, or “cam-out” by offering better surface area contact between tool and bolt. Way back before high-tech torque wrenches, bolt heads needed to be torque-limiting by design. With a slot head or Phillips head screw, maximum torque input is limited by the shape of the screw head. Most of you know that feeling of stripping out a Phillips wood screw when you don’t apply enough pressure to a power drill. While it is frustrating, that feature is there for a reason (and admittedly made worse by using cheap and/or soft screws).

Allen wrenches don’t generally have as much trouble with cam-out as a Phillips or slot head, but they can still suffer given some of the modern developments in cycling. There are two areas in which Allen, or hex-head bolts suffer:

1. In smaller sizes (3mm and below)

2. When using soft or lightweight bolt materials (aluminum or titanium)

If either of the above conditions (or both) are present, your chance of a stripped bolt increase dramatically. This is where Torx can be beneficial. As well – I think we can agree that if we’re going to pony up for an expensive set of titanium upgrade bolts, we’d rather they not be designed to self-destruct by stripping out, just to keep us from over-tightening them.


The Invasion, and How it Happened

Torx first came on to the bicycle scene in substantial numbers with mountain bike disc brakes:

While I don’t really know why this was the first place we saw it, my guess is this: That application requires a relatively high torque given a relatively small bolt head. Manufacturers likely deemed a 3mm bolt insufficient for this task, and opted for Torx. When you consider the even-later introduction of titanium rotor bolts (which are softer), it became doubly important.

Whatever the reason, that decision influenced a whole generation of bike evolution. The size chosen for these disc rotor bolts was T25 Torx. What the heck does T25 mean?

Torx sizing – or at least the names of those sizes – is an odd system. T25, for example, has a distance of 4.43mm from point-to-point. The next size up is T27, and has a distance of 4.99mm from point-to-point. None of that really matters, though, so don’t worry about it. The only thing you need to know is that T25 is the main size used for bicycles. A secondary size that sometimes gets used for smaller bolts (i.e. access bolts for disc brake fluid) is T10. Think of T10 as a good substitute for a 2mm or 2.5mm Allen bolt.

That’s it? We only get two sizes – T10 and T25? For now, yes. Time will tell if there is a need for more. Most big-box hardware stores can sell you a 1/4th inch drive complete socket set. Here’s mine, which ranges from T10, all the way up to the big-boy T50.

Torx in the Modern Day

SRAM was the first company to make the leap with Torx and use it on a large scale for something other than rotor bolts. In late 2009, they debuted the super-light “XX” mountain bike groupset, which featured T25 derailleur limit screws. While I wouldn’t really call this move necessary (i.e. your risk of stripping a limit screw is relatively low), they were sending a message to the market: We like Torx, and it’s here to stay. Shimano got on board with Dura Ace 7900, using T25 Torx chainring bolts:

More recently, Zipp got on the bandwagon by putting T25 bolts on their entire line of Service Course stems, and now the new Vuka Alumina Clip aerobar. While the initial reaction from some mechanics was one of hesitation, my sense is that the feeling is quickly disappearing. Zipp P.R. Manager, Dave Ripley, told me that they felt the market was ready for the move. He also mentioned that with something as safety-critical as your handlebars, they wanted bolts that would offer reliable and accurate tightening over and over again.

The big question is this: As consumers – does it matter? Do you care? Or perhaps: Is the benefit worth the cost of buying new tools?

I personally support the change, with one caveat: on-the-road repairs. To put it simply, most of us don’t think about the multi-tool that sits inside our saddle bag or repair kit. If you have one that is more than a few years old, there is a very good chance that it does not have a T10 or T25 Torx driver on it. If you happen to have a Torx bolt come loose during your ride – you may not be able to tighten it on the side of the road. Zipp has done a good job of accommodating this by supplying a mini 4mm-to-T25 adapter bit with every stem they sell – you just have to remember to put it in your repair kit.

My Crank Brothers multi-tool has a T25 parked next to the flat and Phillips screwdrivers:

The place that I’d really like to see Torx take the lead is on anything 3mm and below. These small sizes are simply too prone to stripping out after repeated tightening and loosening. You see, over time, your tools get worn out. Take, for example, one of my trusty 5mm Allen wrenches:

Over time, the finish wears away, and you’re actually making the tool smaller. This means you get less engagement with the bolt – and more chance for a stripped bolt. With 4mm and above – and especially with steel bolts – this generally isn’t a problem until the tool gets very worn. With 3mm and below, however, you’re at greater risk.

Take, for example, my new-plus-old aerobar setup here. I have a new-school Zipp Service Course stem with T25 bolts, and their original VukaClip, with 3mm Allen bolts:

I’m anal-retentive when it comes to my bikes, so I always travel with one spare bolt for everything on the bike (including these 3mm bolts).

Another place that I think we ought to ditch small hex bolts is on our brake pad carriers. These typically feature 2 or 2.5mm Allen heads:

The problem that arises has to do with our sport of triathlon, and the way we punish our rear brakes. Add up a lot of sweat, salt water, and sports drink – and the entire back of the bike gets glued together with a film of slime. Say you’ve been training all year for your big race… and now it’s time to put those race wheels and carbon brake pads on. You whip out a 2mm Allen wrench to change the pads – only to strip out one of these tiny bolts because it’s seized in place. The best way to remedy this is to use a penetrating spray lubricant and a new-ish wrench… but sometimes you don’t realize that until it’s too late. A switch to T10 Torx hardware would likely solve this problem entirely.

In general, I think companies are still gun-shy about Torx for a couple reasons. First, it’s still “new” to most cyclists, so the manufacturers would be taking a risk by using it. Second, there is the ever-present ham-fisted mechanic who does not know when to stop tightening a bolt (or refuses to use a torque wrench). With Torx, the name is really representative of the product: It allows you to input a lot more torque on the bolt – which also means more chance of stripping the threads. When using a proper torque, the system works fantastic – better than Allen bolts. However, manufacturers have to weigh in their risk of product warranty. For example, no frame manufacturer in their right mind would ever use a Torx bolt for a water bottle boss. Stripping out one of those means replacing an entire bike frame.

One of my favorite manufacturers of bars and stems, L.H. Thomson, recently moved their stems from 4mm hardware down to 3mm. Why? Thomson marketing manager, David Parrett, said it was a calculated move that they (unfortunately) needed to make. Simply put, they had to frustrate a percentage of good mechanics who know what they’re doing – to accommodate the ones who over-tighten bolts and increase the warranty rate. With a 3mm bolt, you’ll strip the bolt head before the stem body… and it’s much less costly to replace a bolt. While I understand their choice from a business standpoint, the mechanic in me gives a sigh of disappointment.


If nothing else, I hope this article serves as a brief education piece on your bike’s critical bolts. If your bike does have any of these new-fangled Torx bolts, take the 30 seconds to check your bike’s saddle bag repair kit. If you don’t have a Torx bit on your multi-tool – get one that does. Finally, because manufacturers read these articles too, let us know what you think in the comments. Do you like Torx? Did you know what it was before you read this? Do you want to see more of it?