Weird Fasteners

June 24, 2005 5:04 PM

Why Do Companies Use Weird Fasteners for Products?

I had to open up a hedge trimmer today and it has these weird fasteners that are not quite a hex key, and not quite a star of david. I see this kind of thing on various products. Why can't companies just use normal fasteners?

posted by Ken McE to Technology (19 answers total)

Uh, you mean torx head screws? They are normal (for some value of normal.)
posted by Zed_Lopez at 5:12 PM on June 24, 2005

Yeah, torx not so exotic any more. Pretty common in automotive applications and found on motorcycles and bicycles, too. More surfaces to engage than allen wrench/socket head screw.
posted by fixedgear at 5:16 PM on June 24, 2005

They're most likely torx fasteners. They're nastly little fawkers if you're trying to remove them from something they've been in for a long time (oooh, let's say like a rusted AMC Jeep), but they're used quite often in assemblylines because a torx fastener stays on the torx bit more readily than, say, a regular bolt. So it makes it easier for the robots to assemble the items.

Cheers,
Ed T.
posted by Lactoso at 5:18 PM on June 24, 2005

They all have their purpose:

• Slot head - the earliest type. Easy to machine using early machining systems (i.e. cutting a groove in a blank head is easier than punching a hole). Obsolete in industrial applications, but it's not any harder to use with manual screwdrivers.
• Philips head - Self-centering and screw driver pops out when tight, making it was good for human-operated powered screw drivers (i.e. the driver screws the fastener in until it slips, then the operator knows it's in all the way).
• Torx - Self-centering and doesn't slip once inserted, making it ideal for human or robotic torque-based fastening systems (i.e. the screw driver is programmed to turn until a certain amount of torque is reached and then stop, yielding much more consistently tightened screws)

Most other custom types exist for the sole purpose of being proprietary, to signify that only professional repairmen should open the item in question.
posted by boaz at 5:43 PM on June 24, 2005

You know, your list isn't complete if you don't include Robertson head.

People actually say that screw driver slipping out of the screw head is a feature? That is a little twisted...
posted by Chuckles at 6:40 PM on June 24, 2005

On Happy Meal toys I have noticed screws with a triangular slot, but I am not sure what they are called.
posted by beth at 6:58 PM on June 24, 2005

Specialty Tools Screw Types will give you a good overview of pretty much every variation you might come across. Also note that some manufacturers will use obscure types in order to provide some tamper resistance and theft prevention.
posted by tumble at 7:06 PM on June 24, 2005

Well, if you're operating a high-power compressed-air screwdriver, slipping out under high torque situations is a huge improvement over the alternatives of breaking the screw head, the driver jumping out of your hand, breaking the driver bit, or ruining one of the fastened surfaces through overtightening.
posted by boaz at 7:10 PM on June 24, 2005

I've also found that using an odd shaped screwhead is used by companies when the don't want you to be playing around with whatever is inside. If it is difficult to open, you are more likely to go to an official dealer for repairs.
posted by GeneticFreek at 7:57 PM on June 24, 2005

you can buy a selection of "funny" hex bits at electronics/diy stores (where each bit is attached to a hexagonal rod that slots into a variety of handles/tools). i have a little pack of around 30 bits that, together with the standard flat and cross head bits, opens almost anything.
posted by andrew cooke at 8:13 PM on June 24, 2005

I'm always astounded that Robertson (square-head) isn't in more use down in the USA. It's more common than common slot heads up in Canada.

Philips is great for its slipping capability. Ideal for drywall, for instance, where you can use a sleeve that causes the driver to disengage when the screw is exactly the right depth (slightly countersunk, but not tearing the paper). It was also ideal for machine assembly back in the time it was invented; not so hot now that we've better ways of measuring tightness.

Robertson is great for not slipping. Ideal for everything except the few special better-use-Philips cases.

I can not fathom why any other hole-style fastener exists. Slotdrive is just stupid. Posidrive and such are just silly. Hex is almost the same as square, but more likely to strip out. And torx exists solely to avoid Robertson's patent (which I'm fairly certain is expired now).
posted by five fresh fish at 8:17 PM on June 24, 2005

So these weird bits are a form of DRM for my tools? How long 'till its a crime to reverse them without permission?

I had an earlier case of this where I went to take the factory radio out of an old Pontiac. It was held in with weird little fasteners that needed kind of a melted bat shape to drive them. Nobody in my entire neighborhood had the right shape to drive those suckers. I drove it down to the Pontiac dealer, asked them to unscrew the screws for me. They said it was a custom fastener meant to stop people from stealing Pontiac radios, you had to be a dealer to get the tool.

Problem was, the thieves just shifted to tearing out the radio along with the middle of the dash, unscrewed it from the back with a pliers after they got it home. Made a heck of a mess. Now instead of just buying a new radio you had to buy a whole new dash to go with it.

Pontiac gave up on the melted-bat fastener, went back to regular screws. The dealer didn't have the tool and couldn't get one either. He advised me to just cut a notch straight across with a hacksaw blade, take them out with a straight screw driver and throw them far, far away.
posted by Ken McE at 8:42 PM on June 24, 2005

I think the melted bat you are talking about is a clutch head screw. Used in the 50-60's GMs, Case combines and more recently HP computers. Snap-on and others have the bits.
posted by 445supermag at 8:51 PM on June 24, 2005

Ken McE writes "How long 'till its a crime to reverse them without permission?"

Already is, at least initially. Most of these screw/bit combos are patented so that no one can easily bypass your supply chain for the first dozen years, it's what makes it tamper proof. Maytag is famous for this in major appliance circles, I once spent over C$100 for a transmission wrench for a maytag washer.
posted by Mitheral at 9:52 PM on June 24, 2005

five fresh fish >>> "I'm always astounded that Robertson (square-head) isn't in more use down in the USA. It's more common than common slot heads up in Canada.

You have the egos of Robertson and Henry Ford to thank for that. If memory serves, he wanted to buy Robertson's screws and drivers (Roberston being a Canadian), but would only order them in x quantity (by the gross or by the hundred, can't remember which). Robertson would only sell them the other way. Thus, no Robertson screws on Ford vehicles, which was a mjor vector for all sorts of manufacturing techniques and tools.
posted by dirtynumbangelboy at 10:17 PM on June 24, 2005

From what Mitheral said, I guess I wasn't as bad off as I felt at the time. I had to fix something in my first PC, a Compaq portable 286. They had used torx head screws, and back then (late 80's) they weren't easy to find. Paid WAY too much for a tool I've not used since.

At least today we get cheap multi-headed drivers to go with these fabulous wrist-saving power tools!
posted by Goofyy at 10:18 PM on June 24, 2005

On preview, dirtynumbangelboy beat me to it. But I didn't know the details, thought it was some turf agreement, like Hellmann's and Best Foods mayo.
posted by Rash at 10:25 PM on June 24, 2005

> Why Do Companies Use Weird Fasteners for Products?

To prevent anyone except Authorized Persons with the restricted magic screwdriver from working on them.
posted by jfuller at 5:07 AM on June 25, 2005

But what of the wood (working/construction/etc) industry? How on earth do you build a deck without using Robertson decking screws? I'd be surprised to find many Canadian woodworkers using anything but Robertson screws.

Machinery, not so much. Wood, fersure.
posted by five fresh fish at 9:29 AM on June 25, 2005