We previously explored Torx in our 2018 article Bit History: The Torx, as we launched our Manta and Mahi driver kits.
It’s hard to keep track of all the different types of screws, fasteners, bolts, bits, and bobs that hold our lives together, from our fridges and phones to cars and planes. If you’ve ever poked around inside a gadget, you’ve probably come face-to-face with a 6-lobed, star-shaped screw.
That’s Torx. It and its new, high-tech cousin, Torx Plus, are the current kings of the screw hill. But what are they, and what makes them so special?
First, a word from our … history lesson, on how we got here: Phillips.
Phillips: Cam-out and Cadillacs
The Phillips (PH0, PH1, etc) or “cross-head” screw as we know it was introduced in the 1930s as an improvement over traditional slotted screws. You know, the ones on outlet covers that constantly slip out. In addition to Phillips being decent at self-centering, a key feature is its tendency to cam out, meaning the screwdriver will slip out of the screw head once the torque, or twisting force, gets too high. This happens because the cross shape has sloped walls, creating a force that pushes the driver up (or back towards you) as you spin.
The bad? “Camming out” is just another name for stripping. The good? Stripping prevents damage to both the screw threads and the actual part getting screwed.
This behavior was actually embraced, becoming important for General Motors. They adopted Phillips across their Cadillac assembly lines because it prevented over-tightening, saving cars and tools from damage. The downside is that cam-out can chew up the screw head and requires pressing down hard to keep the driver engaged. Stripping screws is something we’ve all experienced. Thanks to its popularity, we’re still cursing under our breath, all while it does something it was designed to do.
Torx: Solving the Problem
By the 1960s (and after decades of mechanical frustration), assembly technology had advanced, and manufacturers wanted screws that didn’t slip. Enter Torx (T30, T40, etc), explicitly designed to prevent cam-out, relying on new torque-limiting tools instead.
Compared to Phillips (or slotted or hex screws), Torx has straighter sidewalls and a much tighter fit. And it engages screws at a better angle, greatly reducing that axial force that pushes the driver out. Practically, a Torx bit stays engaged: you don’t need to press as hard to avoid slipping, and you can apply significantly more twisting force without cam-out, with less damage to the screw or tool. This is why deck screws use Torx. They can be zipped in with impact drivers with little risk.
Torx screws fixed most cam-out issues by using a shape that provides constant contact and a near-90° drive angle. This design does away with the self-ejecting tendency seen in Phillips screws, and, as a result, Torx became popular in automotive and electronics assembly, with assemblers able to tighten screws faster, with higher torque, and with less wear.
One important Torx variant is tamper-resistant Torx Security (TR8, TR10, etc.). You might’ve seen these funny-looking screws holding airport bathroom stalls or Xbox controllers together: they’re designed to lock normal folks out. A center post sticks up from the middle of the screw, blocking standard Torx bits from entering at all. The “special” Torx Security bits just have a middle hole cut out to slot over that post, but are otherwise identical, if not just a bit weaker than the solid regular Torx. Security Torx bits fit and function just fine in normal Torx screws, and in the spirit of the most compatibility possible, they’re what we stock our toolkits with.
Fundamentally, we don’t like Torx Security or proprietary screw heads. Of course, if they’re used to safeguard dangerous environments, sure. But to hold game controllers shut? That’s anti-repair.
Torx Plus: New Geometry, Better Force Transfer
While Torx was a huge improvement, it wasn’t perfect. In the early 1990s, we first saw Torx Plus (3IP, 4IP, etc) as a further Torx evolution. It uses a modified lobe profile: elliptical lobes with completely vertical sidewalls, instead of the circular arc lobes of standard Torx. This yields a true 90° drive angle, putting all of your twisting force directly into turning the screw. Not only that, but with straight walls, nothing forces the bit upward. So long cam-out. So long surprise slips.
Beyond the perfect drive angle, Torx Plus also features a larger cross-sectional area at the lobes (the lobes are broader and less rounded). This spreads the contact patch over a greater area, preventing any concentration of stresses that can wear out bits and damage screws. In other words, more of the driver is in contact with more of the screw at any given time.
The overall size of the hole is also simply larger, making it easier to align and seat bits quickly in automated assembly. This also means that Torx Plus drivers require little to no downward force to stay engaged, reducing worker fatigue and error. Torx Plus took the advantages of Torx and amplified them: even better torque transmission efficiency, higher strength, and virtually no slipping, all through clever changes to geometry.
In Torx Land, a Tight Fit Isn’t Always Better
When it comes to driver fit, our intuition tells us that a tighter fit is always better. This intuition wins with Phillips: you should always use the size that fits the most snug.
But physics tells a different story for Torx. The optimal situation is when a Torx driver fully bottoms out, the tip of the driver reaching the base of the screw drive socket.
This slightly “loose” fit that bottoms out will engage all surfaces from tip to top, providing secure contact. In contrast, a driver that fits tight may not insert completely. It’s probably actually stuck partway in, not reaching the bottom. In that case, only the upper portion of the drive surfaces are in contact, which, once you start turning, concentrates all that force on a smaller area. This partial engagement can lead to cam-out damage because the load isn’t spread out.
To illustrate this concept, consider a Torx Plus screw that calls for a size three (3IP) driver. If you don’t have the exact Torx Plus bit, you might try a standard Torx bit: but should you use a T3 or T4?
Turns out, the smaller T3 bit actually works better in a 3IP screw than a seemingly “close” T4. The T4 is just a hair too large. It wedges in partway and won’t bottom out. You’d be turning just the shallow upper edges of the recess, which are likely to strip under load. The T3, while looser, goes all the way in and bottoms out at the floor, engaging much more of the walls.
Of course, the ideal solution is to use the correct bit to begin with. Then you get a snug fit and full engagement by design.
Torx Bits Turn Torx Plus Screws. But Not Vice Versa
There’s frequent confusion about whether Torx and Torx Plus tools are interchangeable.
The answer is: kind of. A standard Torx bit can fit in a Torx Plus screw, but not the other way around. A Torx Plus bit won’t fit in a Torx screw. This is by design. The Torx Plus screw recess is larger, shaped to fully envelop the driver, so it can accept the corresponding older Torx bit, albeit with a bit of looseness.
If you don’t have anything Torx Plus on hand, a same-size Torx bit will usually slot into a Torx Plus screw well enough to turn it. You won’t get the full torque capacity, though, because the Torx bit’s smaller, rounder lobes won’t contact as much surface area. It might cam out if you push it too far. But it’s enough to remove or install the fastener in a pinch.
However, the opposite, using a Torx Plus driver on a Torx screw, doesn’t work. The Torx screw’s opening is narrower, and the Torx Plus bit’s broader lobes simply can’t insert fully. The Torx Plus driver is just too fat to go into the older Torx-shaped hole. If you force it, you’ll probably cam-out. And, if you try to size down, too little of the bit will contact the screw walls, also causing cam-out.
In real-world terms, if you attempt to use a Torx Plus screwdriver on a regular Torx screw, you’ll find it won’t seat—the shapes don’t match. But if you use a Torx driver on a Torx Plus screw, it’ll go in with a bit of play, a looseness that, at first, might feel too loose.
This underscores the importance of using the correct driver design for high-torque applications. But the good news for us in gadget repair land is that if you’re in a bind, your standard Torx bits will do just fine. The small fasteners in our gadgets aren’t usually subjected to that much force: they aren’t able to be torqued remotely as high as, say, something automotive, so they won’t feel the reverse during their undoing.
Torx Plus is Turning Up in All Kinds of Gadgets
Companies like Apple, Google, and Microsoft are all starting to use Torx Plus. Turns out it’s just a really good screw.
Although they were pretty uncommon up until only a few years ago, adoption is speeding up. Even detail-oriented Apple shipped a generation or two of MacBooks that used both Torx and Torx Plus at the same time during the transition. At sizes below T5/5IP, it’s really hard to tell the difference!
Screws may seem minor, but they dictate who gets to open a device, who gets to fix it, and who gets to throw it away. Which is why we pay such close attention to changes like the rise of Torx Plus, and why we want to talk about it.
If the right tool for the job is proprietary or hard to find, repair becomes harder. And when repair gets harder, more devices end up in landfills. As great as Torx Plus is, it can be a barrier to repair for people without a comprehensive kit. Our kits include a wide array of Torx and Torx Security bits, which will do in a pinch, but someday soon we’re going to have to update our kits to include this new generation of screws. If you need them sooner than that, you can always upgrade your own kit by buying Torx Plus bits individually. We’ve got Torx 1IP through Torx 20IP available individually in our store.
Really, our main problem with Torx Plus right now is that it’s a rare sight in people’s toolboxes.
It won’t replace trusty ol’ Phillips anytime soon. Despite its problems, Phillips is ubiquitous, which makes it a good choice for anyone looking to increase repair access. We all have at least one Phillips screwdriver in at least one junk drawer. It’s played a key part in helping everyone fix every thing, which happens to be our main mission. After all, it’s why our logo isn’t Robertson, Torx, or Torx Plus. It’s Phillips, the humble repair champion.
For more Bit History, take a gander at earlier entries about the Phillips, the flathead, the spanner, and the pentalobe. Want more of everything repair? Sign up for our weekly newsletter, subscribe to our YouTube channel, and get involved in your local community.
3 Комментариев
The question this otherwise good article didn't really address is how if a mystery gadget lands on your bench, how do you tell if it's using Torx or Torx Plus screws?
This is similar to the question of telling Phillips and Posix screws apart - but at least the markings on a Posix screw will help identify it.
Arthur Torrey - Ответить
The Wikipedia article denies that the Phillips was designed to cam out intentionally to limit torque; do you have a specific citation for that?
I like the X-ray visualizations of the screw drives.
Apparently the Torx Plus patent has already expired, but perhaps it remains more expensive, e.g. due to a difference in manufacturing cost or just economies of scale favoring Torx (or Phillips).
Fat Pigeon - Ответить
I am Canadian and always buy Robertson screws - Phillips are the worst. In Canada Robertson is king - used everywhere. Torx only used where manufacturer did not want user self repair.
Terry Joevenazzo - Ответить