Why Are There so Many Types of Screws?!

Why Are There so Many Types of Screws?!

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This episode of Real Engineering is brought
to you by CuriosityStream, watch over 2,400 documentaries for free for 31 days at curiositystream.com/realengineering. We have all been there, visiting your local
hardware store like a kid in a candy shop. You arrive at the pick and mix screw section
and you are just overcome with excitement. How could you possibly pick just one type
of screw. Woooooow look at all these screws. Amaaaazing. You have sultry slotted screws, rowdy robertsons,
playful phillips, oh and look at this one a hex screw. You naughty polygon. In your excitement you pick the largest bag
you can find and fulfill your childhood dreams to buy 2 of every kind of screw. Mother can’t stop you now. You arrive home with the glee of a spring
lamb. Oh the assembly that awaits. What joy. Then, to your horror, you open your toolbox
to discover you only have a fat flat head screwdriver that doesn’t even fit the flat
head screws your bought. Your life is a lie. You spent your life studying theory and never
learned practical application. You are no real engineer. Shhh it’s all going to be okay, dry those
existential crisis tears. We are going to learn what all these screws
are for, and how they came into existence. The humble screw is a technology so old that
we cannot easily determine who first invented it, but the answer as best we can tell is
Archimedes who used the helical screws ability to turn rotational motion into linear force
to pump water, though he probably stole the idea from the Egyptians. You can imagine how a screw works fairly simply
by viewing the cross-section at the bottom. This part is essentially a wedge, and when
you force a wedge under something it will lift it up. This wedge shape spirals all the way up the
screw, allowing that force to be applied along the full length of the screw. This idea was used for centuries to pump water,
dig holes, and for pressing the shit out of grapes to make some wine. Then some unknown person had a bright idea. If we can apply an opposing force, we could
create compression to hold two parts together, and so someone slapped a head on one of these
screws that would press down while the threads pulled upwards. Creating an incredibly useful fastener. This idea didn’t really take off until a
method of mass manufacturing them came about in 1797, when Henry Maudsley invented this
metal cutting lathe that allowed for the consistent and precise cutting of screw threads. He even set up a standard screw thread geometry
for his machine shop , and cut all his nuts and bolts to fit those threads, and thus the
chaos started. Several decades of differing standards resulted
in headaches far worse that your annoyance at new phone not fitting your old charging
dock. Perhaps the most notable incompatibility occured
during the great boston fire of 1872 when fire departments from neighbouring regions
arrived to help, only to discoverer their fire hoses didn’t fit Boston’s fire hydrants. [Maybe show XKCD comic] Most of the world has now accepted ISO metric
threads as a standard, although one country is still holding onto the inch as the standard
unit of measurement. A measurement that was legally defined as
the length of “three grains of barley, dry and round, placed end to end, lengthwise”
for 8 centuries until it was redefined as 25.4 millimetres. Because, as we all know, the best in class
is always defined by the second best, but I digress. We can now generally trust that a nut and
bolt with the same diameters will fit, even when mixing freedom units and metric, but
what’s the story with all these different screw heads. Why can’t we just agree on one shape so
we don’t need a toolbox full of screw drivers? The simple slotted screw head was likely the
first type used as it’s easy and cheap to manufacture with a cutting tool, but is a
pretty terrible design for anything other than manual screw driving into wood. Screwdrivers can slip out of sides and you
can turn the screw off its centre axis, which causes it drive into the material at an angle. This was not acceptable for mass production
methods, which as we explored previously, needed a foolproof production method. So Peter Lymburner Robertson designed a manufacturing
process for this square bit screw-head. Which was designed to be easily and quickly
driven home, without danger of the screwdriver slipping out and damaging either the screw
of the workpiece. 700 of these bad boys were used in the Model
T, and it saved Henry Ford about 2 hours of manufacturing time on each and every vehicle. Henry Ford was so happy with the design that
he wanted to licence it and manufacture them himself to ensure he had a reliable and steady
supply of the fastener, but Robertson wasn’t about that money making life and said no. He continued doing this with other manufacturers
for some bizarre reason and now the design is mostly just used in Canada, and so in stepped
Henry F Phillips with his infuriating screw design. He licensed out the design to Henry Ford and
many other people. This conical cross design allowed for a single
screw driver to fit many sizes of screws, was self-centering, and was designed to cause
the screwdriver to slip out of the slot at a certain torque and thus prevent workers
from over tightening it and damage the screwdriver or workpiece. It also prevents you from getting the blasted
thing out of a workpiece with even the slight bit of rust. By 1939 this design was licenced to nearly
every automotive, airplane and rail manufacturer in the US, just in time for the boom in manufacturing
created by World War 2 [1] With the lend lease act, many American designs were sold to their
Allies, and thus the screw design spread even further. Now that most screwdrivers can automatically
limit torque the phillips design is pretty much just a pain in the ass, so other designs
have come to the fore in more recent years. Specifically designed to stop that slipping
called cam-out, like hex screws and torx screws. Let’s compare these two types of screw to
see how their design came into existence. These two screws have the same diameter tool. Both have six points of contact between the
screw and tool. However we can see when we rotate our hex
tool it contacts the screw at a greater radius. Allowing it to applying more torque with the
same force, but the plane of contact is not perpendicular to the circle and that means
some of the force from the rotation of the screwdriver is being applied outwards radially
to the screw. This can damage both tools. With the torx screwhead the angle of contact
is near perpendicular, meaning it can applied more torque without fear of damaging the screw. But ironically, even though this is a great
screwhead design. It was designed to not be used by the general
populace. It was used in Apple’s first personal computer
[2] to make it harder for the average guy with a phillips head screwdriver from opening
up the machine. But thanks to it’s design, Torx screws started
proliferating, and more and more people had the correct tool to loosen it. So someone decided to place a pin in the middle
to make it even harder. Bringing us to an age where our right to repair
is questioned and many random screw designs have appeared to make it harder for us to
take apart our gadgets . Why? Because screw you that’s why. If all these nuts are driving you crazy, you
might just be a squirrel and being a worldly squirrel you probably learn about all the
other types of squirrels around the world. There’s ones with wings, ones with cute
little ears and tails. Look at this ginger one, class. If you want to learn more about them. I highly recommend watching this documentary
titled “Going Nuts” on curiositystream. It’s a beautifully shot documentary that
I really enjoyed. For a slightly more on-brand recommendation,
they also have an exclusive, original documentary series premiering on the 13th of June about
the new race to the moon called ‘Return to the Moon’. You can watch it for free, by signing up to
curiositystream using the code realengineering, or using the link the description. This will give you a month of completely free
access to over 2,400 documentaries and nonfiction titles from some of the world’s best filmmakers. After that first free month you can continue
your access for just two dollars ninety nine a month. As usual thanks for watching and thank you
to all my Patreon supporters. If you would like to see more from me, the
links to my instagram, twitter, discord server and subreddit are below.

29 thoughts on “Why Are There so Many Types of Screws?!”

  1. Re: @0:25… Haha… I'm going to call my GF a 'sultry screw' and a 'naughty polygon' (I bet that'll go over well!)


    BTW, Robertson head.screws are the best. I will fight you if you think it's Torx.

  2. bash on the Imperial measurement system all you want, just remember there are two types of countries in the world… those who use the metric system and those who put a man on the moon!

  3. Coming from a family who's dad has multiple types of screws but one style of screwdrivers, that opening was straight in the feels.

  4. Oh if only we could skip the FAA 8083 section on screws and fasteners for airframes and use your video instead. That would be to easy.

  5. What would you be if you were attached to a solid object by an inclined plane wrapped helically around an axis? o.0

    Screwed! 8-p

  6. What do squirrels have to do with screws? Oh wait, because the PSP has screws and the PSP is like a nut you can play with outside. No joke, Sony actually made a commercial saying the PSP is like a nut you can play with outside.

  7. I loved this one. I feel like I could truly sense the angst and personal nature of your war with fastener standards

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