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Thread: Why Torx screws and not just Hex?

  1. #1
    Spyderco Forum Registered User peacefuljeffrey's Avatar
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    Question Why Torx screws and not just Hex?

    Does anyone know why the prevailing style of screws used for most knives is Torx, as opposed to Hex screws?

    I understand why they don't generally use Phillips head screws -- they SUCK.
    But I have less confidence in the resistance of Torx heads to being stripped than I have in the resistance of Hex heads. I think that ideally screw heads should have triangular slots, because it's hard to imagine that ever stripping, but I suppose that there may be manufacturing issues, I dunno. (Though it's hard to figure why they couldn't easily manufacture a three-sided screw slot if they can make a six-sided one.)

    So what governs the decision of Spyderco to use Torx and not Hex?
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  2. #2
    Spyderco Forum Registered User Orion's Belt's Avatar
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    I believe it is to help deter stripping of the screw head. It will not stop it from happening, but lessen the chance. I haven't ever stripped a Torx head, but have done so on hex heads.

    For the record, some Spydies do use hex. Those being the Tenacious family.

  3. #3
    Spyderco Forum Registered User Evil D's Avatar
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    Actually from a technical stand point torx heads provide more surface area and are less prone to stripping within their designed torque specifications. They strip because of poor fitting bits and gorrilla fingers. Its super important that the bit fits properly and you keep it straight when turning. I guess you could say theyre more prone to accidental stripping. It pays to invest in a quality bit/driver set as the cheap ones arent always accurate in size.

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    Torx were designed to allow the screw to be tightened as far as possible. They exist because people wanted a head that would be more resistant to having the screwdriver spin out. On the other hand, phillips were made to have the screwdriver spin out so that the screw wouldn't be over-tightened, so in that sense, they're the opposite of torx.

    The fact that the screwdriver doesn't spin out of the torx slot means it has an extended life. Hex, in comparison, won't last as long. Hex also aren't meant to take as much torque as torx. With a knife, I imagine the difference in torque is meaningless, but the extended life is definitely a benefit.

  5. #5
    Spyderco Forum Registered User peacefuljeffrey's Avatar
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    While I understand the idea of there being more surface area contact between the driver and the screw with Torx, I don't know why it's needed over what you get with Hex. When the driver is in the head of the screw, where's it gonna go? I don't have so much confidence in the little nubs of metal that bear the turning force. Surface area or not, those little projections have to resist shearing right off when the turning force is applied. With Hex, it's hard to imagine anything stripping the six-sided well inside the head. If the force were going to go anywhere, I'd think that the entire head would blow out! But I'm sure that the screw would strip before that happened.

    Does anyone know why they don't do a three-sided drive system?
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    I think because a three sided system just is not common and does not look that good.

  7. #7
    Spyderco Forum Registered User The Deacon's Avatar
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    Quote Originally Posted by Stefan Roth View Post
    I think because a three sided system just is not common and does not look that good.
    Either that, or because it would be inefficient in a production environment. Aligning a three sided driver with the screw is more time consuming that aligning a six sided one.

    Between guns, model railroading and R/C modeling I've worked with plenty of small screws. Slot, phillips, allan, and torx heads all have their good points, but all will strip if excessive force is used.
    Paul
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    Spyderco Forum Registered User peacefuljeffrey's Avatar
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    Seems to me that if a triangular system were used, it would be awfully hard to strip. It seems intuitive that the more acute the angles inside the head, the more metal would have to be pushed out of the way by the driver. Plus, I think that a triangular hole in the screw head would be cool looking. I wish that had been what caught on, instead. Torx gets the job done; it's just that it's not everything I would want.
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    Spyderco Forum Registered User JNewell's Avatar
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    Historically, experience with hex-type screw heads shows they are much easier to round out than a Torx head. Add to that the following problem and it's pretty much a slam-dunk IMO: the actual size of the hex recess varies in general by country of origin, or more specifically whether the screw is US-domestic or foreign. Foreign fasteners tend to be metric. US hardware tends to be SAE. That's not a hard and fast rule, but it is still common. What that means in real life is that it is very likely that people will use the wrong size wrench on the screw, which makes rounding out the screwhead even more likely.

  10. #10
    Spyderco Forum Registered User Evil D's Avatar
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    You probably can't strip a triangle head screw unless you use the wrong size bit, but they're just not common enough to use. I've only even seen them in a few random applications. Square head screws would be another option though.

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    Spyderco Forum Registered User yablanowitz's Avatar
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    I'm pretty sure Paul is right. In a production environment, aligning a triangle driver to a triangular hole simply takes too long, and time is money. Even if the screws and drivers were free (which they're certainly not), it would add to production costs on the time factor alone. As for the lobes of the Torx driver shearing off, not within the torque specifications of the fastener. If you exceed those specs, the fastener will fail no matter what system is used.
    I don't believe in safe queens, only in pre-need replacements.

  12. #12
    Spyderco Forum Registered User jackknifeh's Avatar
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    Quote Originally Posted by Evil D View Post
    You probably can't strip a triangle head screw unless you use the wrong size bit, but they're just not common enough to use. I've only even seen them in a few random applications. Square head screws would be another option though.
    How do any kind of screw head get made? Is there a mold or are the holes cut somehow. Straight (common, slot) are easy because the slot goes all the way across. Many of us have used a dremel to "repair" stripped screw heads of other types. One thing that may be considered when designing screw heads or bolt heads is how far do yo need to turn the tool to get it to fit on the bolt or into the screw. Slot screws require the screwdriver to be turned 180 degrees to change the position of the driver in the screw. A hex screw has 6 sides meaning the tool would only need to be turned 1/6th of a rotation to reposition it. A triangle screw head would require the tool to be turned 1/3rd of a rotation which is twice as much. Not a big deal with straight screwdrivers but consider socket wrenches. Have you ever been working on a screw or bolt with a socket wrench in a tight area where how far you need to turn the tool to reposition it in the screw or on the bolt is very limited? Car engine for example. Not a problem with knives of course but when screws are designed and manufactured they probably aren't make just for knives. Does that make sense?

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    Spyderco Forum Registered User Stephen's Avatar
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    The Kreg wood jointing system uses a square drive screw. They are very good & positive. Some stainless steel deck screws are also square drive & you can crank the head right off them before any sign of the square drive slipping, deforming or the driver jumping out.
    O.

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    The square drive are called Robertson and very common in Canada, almost every wood screw is made of it. There's some history on why it wasn't popularized.

    At this size Torx is actually very good at resist stripping, when they are used on cars however that's another story.

  16. #16
    Spyderco Forum Registered User Evil D's Avatar
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    I'm betting almost every seat belt bolt you find on any car anywhere is a torx head bolt. Granted, they're huge and you'd have to really be sloppy to strip one.

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  17. #17
    Spyderco Forum Registered User
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    Its torx because its easier for spyderco to take the knife apart not you.

  18. #18
    Spyderco Forum Registered User
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    Quote Originally Posted by Evil D View Post
    I'm betting almost every seat belt bolt you find on any car anywhere is a torx head bolt. Granted, they're huge and you'd have to really be sloppy to strip one.
    They are actually very easy to strip, both the bolt head and driver, especially if there are any sign of corrosion (i.e. ones on outside).

  19. #19
    Spyderco Forum Registered User Evil D's Avatar
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    I've twisted a few bits before on seized up bolts but i've never stripped the bolt.

    SHARPEN IT LIKE YOU LOVE IT, USE IT LIKE YOU HATE IT
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    Official plea to Sal: Can we PLEASE get a DLC Yojimbo 2? PLEASE!!?

  20. #20
    Spyderco Forum Registered User
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    Picture this, T55 front bumper bolt, 200lb of me standing on the breaker bar so the bit won't cam out, my buddy of same size turning the bar with a pipe.

    No the bolt didn't come out, we had to drill it in the end.

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