So people often criticize me for using
the lowly drywall screws to hold a lot of things together.
Especially when I built my sheds
I thought I'd do a test comparing drywall screws
against a few other types of screws
to see how they hold up. So the screws are
all about 2 1/2 inches long.
This is a number 7 drywall screw,
a number 8 wood screw,
and 2 deck screws The difference is
this one has a self counter-syncing head
and this one doesn't.
So what I want to test is how hard these screws can pull.
So I'm gonna put this screw in this piece of wood.
I've pre-drilled some holes in there,
and I'm gonna screw it into here
and clamp it against here.
And I’ve got this all equal distances here so
this here is my fulcrum,
and this is 1/3rd distance as it is to here.
So whatever force this screw pulls,
it's gonna exert 1/3rd of that force
onto my bathroom scale.
So, my scale reads in pounds
and I'm gonna start this screw
just with an impact driver and I want to see
what the maximum holding is.
So, now that it's started,
I'm gonna finish it with a regular screwdriver
just so I can see control this more carefully.
So right now we're at 40 pounds.
So that means we're pulling at 120 pounds right here.
And let's start tightening this up some more.
60.
Now we're at 70.
Let's give it some more. And you can see
the head is sinking in. That is always the
problem with these screws is,
it's not how well the thread holds,
it's that the head starts sinking into the wood.
75, but it's yielding.
So I think we should only count that as a 70.
And let's give it one more twist.
Appears to settle at about 75 pounds.
So this drywall screw
gives me 75 pounds here.
So, 3 times that right here
would be 225 pounds, so it's pulling 225 pounds,
and it's limited by the head here.
All right, next comes the regular
2 1/2 inch, number 8 wood screw.
And I'm gonna use a new hole for this one.
OK, so now let's finish up with a screwdriver.
60.
Still at 60.
60.
Maybe 65 here, but we're already sinking way into the wood here.
It appears to have settled at about 70.
And now for the deck screw without
the self counter-syncing head.
So the maximum I can get this screw to hold at
is 75.
And now the deck screw with the counter-syncing head.
Wow, that screw turns easy.
And it really sinks into the wood
and the best I can get here
is 60 pounds. And I think the problem
is this counter-syncing head is
just keeps digging into the wood.
And it seems to have settled down at 60 now,
so I'll count that as 60.
Now you need to really repeat experiments
to be certain of anything, so I put the drywall screw
in here again and the scale settled at 90.
So the 2nd test with the drywall screw is at 90 pounds.
So I've just drilled another series of holes in here,
so now I can flip my test piece
and do this again. Because it's important
to repeat this and to do it with the same piece of wood
because the spruce really varies a lot.
So, after a whole bunch of repetitions,
and averaging the results, the drywall is
averaging at 82 pounds, the number 8 at 73,
the deck at 75, and the self-tapping at only 69.
So, none of my screws actually pulled out on the thread.
And I think what gives the drywall screw a slight advantage
is the shape of the head, which is much flatter.
Because this sort of shape is a bit more like a wedge
so it drives much more easily into the wood.
That this deck screw did particularly poorly because
it has these little ridges on here, which help cut
a counter-sync, which of course gives the head
much less support. and it also has a bit of a
different angle. So it's all the shape of the head,
and the drywall screw has a slight advantage on here.
But you can't even be sure if these results are
necessarily statistically significant because
I found quite a variation recording the values
on the piece of wood so
the readings on this side of the piece of wood
averaged 80 pounds and the readings on
that side averaged 69 pounds.
And I tried to vary where I put the screws in so
that I would remove this bias,
but the piece of wood itself certainly has
quite a variation because the growth rings
are further apart on here than on here.
So you have a much more of this harder
summer growth material here than you do here.
And that made more of a difference
than the screw heads.
So, if anything, the drywall screws are actually
a slightly better wood screw.
And if you want things to really clamp together,
don't use the self counter-syncing deck screws.
So there's also the question of how brittle
are these screws. So I'm just gonna clamp these
screws in my vise, one at a time, and bend them over
to see when they break.
So that one just broke right where
that device.
Next this one.
About the same.
deck screw.
That one is doing quite well.
And another deck screw.
So I broke a few more screws.
The drywall screws all snapped.
One of the regular number 8 wood screws
actually was about to break but it went to 90 degrees
and hit the vise.
But the deck screws did actually quite well in this regard.
Both of those bent to 90 degrees
without being near cracking.
A more common way for these screws to fail is just
for the heads to pop off of them.
So I've got 2 screws here, a drywall screw and a wood screw,
and even though the drywall screw actually
has a bigger head,
it's only a number 6 screw and this is a number 8 screw
with a smaller head. So, let's turn both of these
to strain to the wood and see what happens.
And even though this is a really hard piece of ash wood,
that screw just went in and sank below the surface.
Next, the drywall screw.
And this screw has just torn apart.
So that number 7 screw, with a big head in the hard wood,
it just tore right apart.
But if you're working with soft woods and you're
worried about splitting it, a small screw with a big head
can be a big advantage. But either way
I've had regular number 8 screws and drywall screws
have the heads pop off of them.
And it really depends on the application
which screw is best.