Wood Screw Sizes Explained – A Beginners Guide

– 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. (upbeat music).

As found on YouTube

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