UCMJ112a: Some of it has to do with torque requirements. A hex, or allen, head can more easily handle higher torque than a phillips.
Some of it is security related. Philips screwdrivers are super common. But the torrix keys with the hollow end arent.
hawkeye18: As usual, there is a relevant XKCD…
Automod appeasement edit:
At one point, there was only one type of screw. I’m no screwolologist, but it seems fair that the straight slot would’ve been that one type.
Its ups were that it was easy to manufacture and it was easy to make a tool for it, but anybody who’s used a straight-head knows it’s a terrible, terrible screw head.
So somebody set out to make a better one. I’ve no idea if I’m right, but I’m gonna guess it was a guy named Phillips. So he said, if one slot was ok, then two slots should be better! But anybody who’s used a Phillips screw knows that they come with an appallingly low torque limit before you now have a conical-head screw that’s impossible to do anything with.
So somebody said straight heads suck, and phillips heads aren’t much better, so I’ll make one with some more meat in the tool and straight sides so rounding off and breaking tips wasn’t such a concern. Thus, the Allen head was born. Except that allen/hex heads, below a certain size, are even easier to round out than Phillips heads were, and it’s fucking impossible to get the hex key in there straight/to full depth in the fastener.
So somebody said, that Allen guy was on the right track, but he didn’t go far enough. So the Torx bit got invented.
But then, people said that Torx was too complicated and it’s impossible to tell the difference between a T25 and a T27 and oh my god why are there so many choices? So we went back to basics and saw if we couldn’t improve on the Phillips design, which beyond its propensity to snap tips and round off fastener heads wasn’t a *bad* design. So we got stuff like JIS, which is virtually identical to Phillips but designed to destroy your phillips bits, and Posidriv, which is the bane of my personal existence because they’re designed to never, never strip while tightening (which they don’t), but to always always strip immediately when removing (which they do).
So that shit got real complicated and somebody said, guys, guys, you’re making this too complicated, eh? What if we took an Allen, which is ok but has too small a load-bearing shoulder and too-great leverage angles, and simplified it, eh? And the Robertson (us Yanks call it a square bit) drive was born. And it was good.
But somebody saw that the construction industry was using a messy hodgepodge of phillips and robertson screws and said, what if we combine them so construction people don’t have to buy so many different bits? So now there’s a combined R1/#2 phillips bit and screw. I guess that guy never got told about Torx bits, but hey, whatever. So now the construction industry is using an even messier hodgepodge of phillips, robertson, torx, and combi-drive bits.
And then, electronics came along, and at some point electronics manufacturers decided that we lowly consumers couldn’t be trusted/were too dumb to open their electronics, so anti-tamper bits had to be made, because everybody had tools to open the bits that were already around, for the most part. So they made those, starting with the Torx bits with the little posts in the middle, but it turns out those are pretty expensive to manufacture so they started making tri-wing screws, and those dove-tail head screws and the two-post screws and etc. etc. etc. because all the same shit that happened in the 10 paragraphs above happened in the anti-tamper-bit world all over again.
Over time each industry sort of settled on certain screw type heads for certain applications, because as there was no “perfect” screw head each type had its strengths and weaknesses, and everybody is firmly entrenched in their own screw head system, and there is *very* little hope of ever unifying everybody, because there’s a lot of money in it now. That doesn’t stop people from trying, though – but since they don’t understand the market dynamics and why there will never be such a thing as the one true screw head, all they do is just add yet another type to the mix, confusing everybody just that much more.
CaptainAlphaMoose: In addition to Skatingraccoon’s answer, many companies develop their own screws or other methods of attachment for their products to make it harder for the consumer to repair the item on their own. A proprietary screw needs a proprietary screwdriver, and if the company that makes the screw doesn’t sell the driver, then it means people have to go to the company for repairs, which allows the company to charge them more than it actually costs to fix the product.
Nowadays, smartphones are growing more and more proprietary, and the reason is so that it is more difficult to fix a damaged phone. With some of Apple’s earlier iPhones you can see the unique shape of the screw: (https://goo.gl/images/sTQqgN)
Although apple did not create the 5-point screw, when they made the iPhone 4s they recognized that it was a very uncommon fastener, so they have used it to make their iPhones ever since.
As the industry is racing towards thinner phones with larger screens and smaller bezels, some manufacturers have removed external screws altogether. The Google Pixel for example, has no screws on the outside. The Samsung Galaxy S7 Edge is another phone without visible screws. This is achieved by using an adhesive to fasten the screen to the frame, which saves space, and makes self-repairs much harder than before.
That’s just the relation to smartphones though, in construction and industry there are many other applications for unique screws. A little-known fact about screws is that screws with more vertices and angles in the bit design grip the driver better. For example, if you had a screw that had a bit shaped like an octopus, that would give the drill bit 9 points to transfer energy into the screw (8 legs and the head). If you had a screw with a bit shaped like a snowflake, it would be even better. The problem with forcing a lot of vertices into the design of the screw/bit is that it becomes easier to break the screw/bit, and the time/cost of production increases. That’s why there are so many kinds of screws, so that consumers can choose the right one based on what they’re doing and what their budget is.
Hope this helped!
schalk81: The first screws had a simple slit. When automation began, the Phillips screw was invented because it is self centering. The sides are angled, so if the first machines applied to much torque, they would slip rather than break.
When machines got torque limiters, there was no need for angled sides. Pozidrive (pz) screws were developed. They only have small angled slits to make them slip should too much torque get applied.
Later came hex and torx screws. They do not slip anymore, so the torque gets transferred completely and they break without efficient torque limiting.
bob4apples: Some things that determine the type of a screw head:
* How hard it is (or was) to manufacture
* Patents and copyrights
* industry inertia
* what tools the installer or maintainer will have
* Whether the screw will be installed by a robot
* How much force does the screw have to withstand
* How much of the screw head can stick out of the surface
* The size of the screw
* other environmental factors (expected corrosion, paint, hard to reach etc)
Skatingraccoon: Different screws have different purposes in the construction world. Same thing with nails, and tools in general.
rwestca: Canadian here, back in the 80’s We used to make and ship wooden crated product to the States. We used to use [Robertson Screwdriver](https://www.thomasnet.com/articles/hardware/robertson-screwdriver-history/) screws ( square heads and really only used in Canada) to close them up. Not being total pricks, we used to include the Robertson driver inside the crate.
Tallyfeo: It has to do with application. A simple flat head or Phillips is mostly used to just do a simple fastening. Allen is more for fastening with more torque, let’s say you’re going to machine a part and are fastening to a fixture, you would feel more comfortable using Allen set screws so your part doesn’t bounce around.
Some of the other screws are more rare so someone doesn’t come along and unscrew anything.
MikeMcK83: Another angle people are not really covering.
The world wasn’t always as it is today. Transportation of products was far more difficult and expensive.
Things like screws, bolts, and fasteners are fairly cheap to make. People making more complex items would either make these fasteners themselves, or get them from someone local.
Now expand that idea across the entire world.
With information and products being shared more everyday, there is less variation. However habit is a strong motivator. If my manufacturing process is working smoothly, why change?
In all honestly is surprising there are not more variations.
On a side note, this expands to many things. Recently I took a truck driving job. I found it really odd how many different warehouses, even by the same company, have totally different procedures in the way they do logistics. Unless I’ve been to that exact warehouse before, I have no idea what policy’s and procedures they will have.
What makes things even more complicated is that everyone assumes that things are done the same everywhere, so there’s an assumption I should know what to do.
You’d think there’s one best way to do things, right?
scurvydog-uldum: Far more than you ever wanted to know:
Flathead screwdrivers suck, but they were something you could make with a hammer and anvil and forge. Philips (the real ones) were designed before power drivers with torque control were invented.
There are a zillion modern designs to provide greater torque limits with reduced material (weight/space/size) that view standardization as an accomplice to theft. They are designed to be difficult to unscrew without the exactly correct driver, to deter theft.
WinstonCup28: I do remodeling. I think this all the time. Specially when I have to go behind the local handyman and fix his jerry rigged “improvements” *sidenote* it’s scary how common it is for fly by night people to come in and do some real shitty or dangerous work and get paid for it. AND screw the homeowners out of ton of money.
But anyway my favorite thing is trying to take something loose and there being 5 types of screws in it. Like wtf? Did you really change bits 5 Times? Were you laughing at how the next person to come behind you (me) was going to be cursing at how aggravating this was going to be?
PA2SK: I am a mechanical engineer. I have to select various fasteners every day. There are all different advantages and disadvantages to different types of fasteners, you could probably spend hours going over everything. To try and simplify to some extent.
Slot screws are the most simple but the screw driver is prone to pop out of the slot and it can be difficult to put a lot of torque on it.
Phillips screws improved the ability to torque it and helps to center the screwdriver so it can’t pop out at much. It’s also more tolerant of off-axis applications, however the screw head needs to be deeper and it’s still only suitable for low torque applications.
For higher torque applications with larger size fasteners you need a wrench. This gets into hex bolts and socket head screws (allen screws).
Allen screws you can apply more torque than with a screwdriver however the head still needs to be pretty deep and it doesn’t work well in applications where it will get dirty or greasy because the socket fills with gunk and is unusable.
Hex bolts are good for all size fasteners from small to very large and work well in dirty environments.
Screws can have an advantage in tight places where a wrench won’t fit.
Specialty screws like torx can be good for security purposes, to prevent people disassembling stuff, or to apply even higher torque to a fastener.
There’s a lot more to it than this but this is just a simplified explanation.
6-20PM: As mentioned by others, specific torque requirements necessitated the improvements in the mechanical interface between driver and screw/bolt, but additionally robotic insertion and fastening required changes in head design to make it easier for robots to hold the screw/bolt and fasten.
pyr666: flatheads are the oldest and exist because they’re easy. philips were made to work for power tools (flatheads slip out too easily).
hex screws are easy to screw in because they can’t slip, but they’re comparatively difficult to manufacture and each key only works for a specific hole. they’re also nearly impossible for machines to interact with (many hex screws you encounter have a nut-like outer rim to deal with that)
pozzowon: First there was the flathead. Then someone thought “maybe this shape will make manufacturing lines faster” and came up with the Philips. Then some Canadian thought “Philips heads tend to strip, what if I can combine the benefits of flatheads and Phillips?” and came up with the squared head…….. That’s all I’ve got.
RearEchelon: Some of them are good for certain situations that others aren’t. Philips, for instance, is used a lot in automated lines because it’s self-centering (get the bit near the center and it goes into the recess on its own). Slotted, or flat-head, screws are good for nothing, however, and should be retired (I hate them).
Other reasons are that the entity who invents a new type of screw refuses to license it to other producers (Robertson).
Bobjohndud: Sometimes, one screw type may be better in some cases than another. and some screws were made to prevent self repair.
vorpalblab: I remember reading that the first use of screw fasteners was to put plate armor together in cases where it would have to be disassembled, otherwise the usual rivet was used. Somewhere between the 12th and 13th centuries.
they were slot head.
FormalChicken: Ugh. This old thing again.
Slotted (what is called flat head) is easiest to make but is not self centering. Phillips is self centering. Robert’s (square) can take a higher torque. In machine settings, hex is cheap and easy to make, but star head can take repeated torquing easier without stripping.
Mix in proprietary and security, one way screws, etc… You’ll hit the total number pretty easily.
gumout: Over the years, screws have been improved. But since you’re not going to replace all of the old screws in your house every time a new generation comes out, you’re going to need screwdrivers of each generation in your box and consequently, there will never be a standard.
But don’t listen to me. This guy is the master. https://youtu.be/N3jG5xtSQAo
NoRealAccountToday: First, realize that all screw types were not invented at the same time. They evolved over several hundred years. As such, both the machines used to make them, the usage of the fastener, plus the method by which the fastener was to be installed caused various mutations and new development over the many years. The first heads were “slot” (“flat”). Simple to make, and a simple tool to install them. Look at Phillips head. They were designed to be installed by powertools and specifically to “cam out” (release) when tight. This stopped the heads from breaking off. Look at Robertson (“tapered square”) They hold on the driver tip so you don’t have to hold the screw with your finger. Many, many more evolutions…each bringing a specific set of features. Why not standardize on the “best”? Often, there is no “best”. And, some fasteners are much more expensive to make.
narwhalyurok: During the industrial revolution inventors were the entrepreneurs of their era. So I would imagine Mr Phillips, Mr Allen and Mr flathead each invented and manufactured their own fasteners and tools to use with their fasteners.
TheRealMrTrueX: Different screws and heads are for different materials and torque pounds. Phillips heads are a + so that when overtorqued you strip the head vs snap the screw I’m half. Look at an Alan head screw , it’ll.tighyen forever u til it snaps. Etc etc for every other screw
gridzbispudvetch: Tech companies (for example) want their products to be really difficult to disassemble so you have to pay them to get a repair if it breaks.
BeUnwise: I know that each have their advantages and disadvantages in machining and construction, but specifically the “Phillips” head (AKA Cross-head) screw which is most common is often misused.
1. It has a notoriously low torque point, so it strips fairly easily. However, this is specifically needed with some industrial and automated applications, where engineers would rather have the screw strip at a certain torque applied by error rather than apply more torque and damage the item in question.
2. The Phillips is self-centering, so when an automated drill drive a screw in, all of the torque is evenly centered and distributed. Again, essential for some automated applications.
So often the Phillips screw is used where higher torque would be helpful, but because of its availability and popularity it’s often encountered in places where it’s low torque become an unwelcome hassle.
Not an engineer but that’s the general point.
SkorcherX: Technology. Phillips we’re designed in an era where drills had no clutches. So the bit needed to cam out once the screw met it’s torque setting.
With all modern drills having sophisticated and adjustable clutches you will find more and more fasteners designed that can take advantage of higher torque settings.
Self drilling and counter-sinking fasteners have pretty much become industry standard.
kstruckwrench: Get a good impact driver with good bits. Learn to use it well. People will think you are a genius.
big_d76: It’s not flathead, it’s slotted.
You can have Phillips flathead, hex flathead, torx flathead.
It describes the head geometry of the screw, not the drive.
buddhabuck: Essentially for all the screw head types, you can make a statement like “straight screw heads are easy to manufacture, but with power tools there is a strong tendency for the bit to slip out of the slot and mar the work surface.”
or “Philips heads won’t slip out under power and will cam out rather than over tighten, but they will strip easily making it difficult to remove. You have to push in while screwing out.”
or “Robinson heads won’t slip out, won’t strip, and work well with a tortion clutch to prevent ovdrtightening. Too bad Robinson was stingy with his patents so no one supports his screw heads outside of Canada”,
or similar “this screw head is good for these reasons, but is bad for these other reasons.”
Picking one standard would work well for some things, but not others.
Alienwallbuilder: Also a thought as time goes on technology gets better and therefore better screws are invented, there probably was a time before screws, then the minus head pattern was designed then the plus head(Phillips) and so on and so on.