- In today's video, we're simplifying the complex world
of wood screw sizes, types and options.
Plus you'll have a chance to download
three different charts to help you make sense of it all.
Just so everybody's starting from the same place,
we need to first briefly talk about
the anatomy of a traditional wood screw.
Starting at the top,
we have the screw head, the shank, the threads and the tip.
Now each one of these can vary
as we'll see later.
There are four main measurements
that can be taken from a wood screw,
the head diameter, the shank diameter,
the thread diameter which is also called the major diameter,
and then the root diameter also called the minor diameter.
The head size for wood screws is sometimes labeled
as a max measurement on screw charts.
For example, the number six or 3.5 millimeter screw
has a max head diameter of .279 inches or seven millimeters.
It's most likely labeled as a max size
because a lot of wood screws actually have smaller heads
than the max size diameter.
Next is the shank size.
This is the diameter of the smooth part of the screw.
You will also notice that the first two sizes
of traditional wood screws
generally don't have smooth shanks.
That's simply because they're just too small for one.
Next is the thread diameter,
this is also known as the major diameter.
This is the measurement
from the outside thread on one side,
to the outside thread on the other.
The last measurement is called the root or minor diameter.
This measurement is taken from the point
in between each thread.
Moving on, the next important thing to know is TPI
or threads per inch.
This is similar to teeth per inch on a jigsaw blade,
but threads per inch
are basically the number of threads per inch
of screw length.
Lastly, to finish off this section,
we need to talk about how the length of the screw
is actually measured.
But in order to know that,
you first must know a few things
about the different types of screw heads available.
Let's look at three of them.
The first one here is a standard flathead
and it's characterized by, well, you guessed it a flat top.
And the sides are actually angled at 82 degrees
which allows for the screw to be countersunk.
The second one is the pan head.
These are the most common of all the rounded top screws
and it's characterized by a broad rounded top.
The last group combines the previous head styles together,
and this one's called an oval head.
So why did I show you these three?
Well, because each one of these
is actually measured slightly different than the other one.
The rule to determine the screws length,
is the amount of screw
that sits beneath the surface of the wood.
For example, this two and a half
or 63 millimeter long flat head
is measured from the top of the screw to the tip, why?
Because this screw's designed to be installed flat
or flush with the surface.
However, the other two screws
are measured from a different starting point.
If we look at them now,
both of the screws I have,
are an inch and a half or 38 millimeters long.
But as you can see this one here is actually taller.
Why is that?
Well it's because for the pan head,
the inch and measurement
is taken from the underside of the head.
Again, once this screws installed,
the head will remain above the surface of the wood.
Now, as far as the oval head,
this one will be countersunk up to about the halfway point,
leaving the rest of the head above the surface.
Why are all these things important to know?
Well, it's the foundation to understanding the numbers
on the side of a screw box,
or a bolt or machine screws for that matter.
And speaking of a machine screw,
let's start there for our first example.
Marked out on the front the package,
is three numbers.
An eight, a 32 and an inch and a half.
The first number is this screw's diameter,
which in this case is a US gauge number eight
which has a shank diameter of five 30 seconds.
The second number is the TPI or threads per inch.
Here in the US, for every inch of thread length,
there is a certain number of threads.
And for this screw, that is 32 threads.
The last number is the length of the screw.
And as we already covered,
that measurement is taken from where the head sits flat
to the surface, to the tip.
Because metric has used so much as well,
let's quickly look at a metric machine screw.
This time instead of having the gauge number,
like a number eight,
we have a diameter size noted as an M6,
which is a six millimeter diameter screw.
The second number is not threads per inch,
but rather a measurement between the threads
or millimeters per thread.
And the last number is the length,
and in this case, that's 25 millimeters.
So now that we looked at the numbers on a machine screw,
let's go ahead and look at the numbers on a wood screw.
Here on the front of the package,
you can see that there are only two now numbers this time,
the gauge and the length.
In this case, if the TPI is not listed,
you can assume that the screw
has the standard number of threads.
And for a number 10, that is 13 threads per inch.
Up to this point, we've covered almost everything
except for the different types of drive options.
Here in the US, there are three types of drives
most commonly used.
And the first one is a Phillips drive,
the next is a square drive and the last is a Torx
or better known as a star drive.
Phillips is still widely used,
and for the most part, they work great
just as long as you use the right size bit for the screw.
Now, when you're looking for a more positive connection,
the star drive does provide that
with very little chance of stripping the screw
under high force.
And of course, last but not least,
is the square drive is this two provides a great connection
between the driver and the screw.
Bottom line, if you're gonna be installing a lot of screws
like say for a deck or a bigger project,
choosing a bit or a driver
that has a really secure positive connection,
is gonna be the way to go.
And I think in that case,
it's gotta be the star drive.
Moving on, let's quickly talk about
pre drilling and correct screw depth.
First, screws holds securely because of the threads
not because of the shank.
Therefore what pre-drilling does,
is removes the thickness of the shank material,
so not the threads can grab the wood
for a very strong connection.
Now, I won't get into the specifics
about how to pre drill
because I've already done a video on that
and I'll leave a link up here
and down in the note section.
Second, as a general rule of thumb,
whenever you're screwing two pieces together,
the screw should enter
at least halfway through the thickness
of the material you're screwing into.
For example, if you're screwing two pieces
of three quarter inch,
or 19 millimeter flat stacked together,
you want to choose a screw length
that will drive at least halfway through the bottom.
So in this case, the closest screw length
would be an inch and a quarter or 31 millimeters.
Before we end for the day,
let's look at the available sizes
for the six most common traditional wood screws.
We'll check out some of their uses,
and then we'll cover a few of the nontraditional screws
just for fun.
Out of all the available screw sizes,
the most common or the number four,
six, eight, 10, 12 and 14.
The number four is used for very light projects,
like installing small hinges or on boxes
or other smaller woodworking projects.
They're available from threes of an inch
to an inch and a quarter.
The number six will be used for things like larger hinges,
drawer slides and other woodworking projects.
Their available sizes are a half inch to an inch and a half.
The number eight is the most common size used
and it's a great general purpose screw.
The number eight is available
from a half inch to three inch.
The number 10 is used on a lot of outdoor projects
like decks porches and that's just to name a few.
They are sized from three quarters of an inch
to four inches.
And lastly, the number 12 and 14
are used for heavy duty construction
when size does matter.
These are available from three quarters of an inch
to four inches as well.
As far as they're nontraditional screws,
there are a ton out there.
So let's quickly look at seven of them.
The first one is a bugle head,
which is very similar to the flat head,
but as you can see,
the head is shaped more like a bugle.
These are primarily used for drywall and duck screws.
The next screw here is the same gauge and length
as the one I just showed you,
but this time this one has a square drive
and the head is much smaller.
This is a great example
of how the same gauge and length screw
can have a smaller head diameter,
which makes this screw less noticeable once installed.
The third screw is called a trim head screw,
and they are characterized by a small diameter head.
Both of them are great to be used as a finished screw,
meaning that once the screws are installed,
you're actually able to see it in the end product.
The other thing to point out about the screw
compared to the last one, is the tip here,
where you could see that some of the material
has actually been removed.
What this does is it helps the screw
to act as a drill bit,
cutting material as it's being driven through the wood.
The option is available
on many other types of screws as well.
Next, we have a modified truss head,
which is basically a truss head with a flat washer attached.
This type of screw has a few uses,
but in woodworking, it works extremely well
at attaching drawer fronts, why?
Because it has a very big head,
which means that it can hold some pressure,
but at the same time,
it has a flat enough profile that it's not offensive.
The next screw is known as a pocket hole or a kreg screw.
These look very similar to a modified truss head,
but are used along with a kreg jig system.
The last group is a premium exterior screw,
this is a stainless steel screw
that has some really crazy threads
to help reduce splitting among other things.
This bit is fitted with a star drive
which is arguably the best drive that you could have, why?
Because it creates such a positive connection
that you have a very little chance
of that screw stripping out.
Also, if you look at the underside of the head,
you can see what are called nibs.
These are added pieces of material
that help countersink the screw.
To better help you understand today's information
and so that you can access
and reference of that information later on,
I've made you a few free downloadable charts.
The first chart here
looks at the six most commonly used wood screw sizes.
It shows things like countersinks size,
shank diameter, threads per inch, pilot hole sizes
as well as the size of the drivers needed for each screw.
At the bottom of the page,
you can see another chart that shows the metric equivalent
to the US gauge as well as the pilot hole sizes.
The next chart will help you to convert
millimeters per thread, which is used in the metric system
to threads per inch,
which is used in the imperial system.
And the last chart I have for you
helps with all conversions,
from fraction to decimal to metric.
All of these charts are available for free on our website.
Just use the links down in the notes section below.
Thank you so much for watching as always,
and I hope you were able to pick something up new today.
Thanks for watching,
see you in the next one.
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