What Is the Diameter of a Number 8 Wood Screw
Types of screws (and when to use them!)
If you've ever been to the fasteners section of a hardware store of home center you know how intimidating this experience can be. You may only need a few screws, but what kind should you get? There a bazillion different kinds of screws and there is no way I can cover them all, so I'll will give you an overview of the most common types of screws and what you will need for woodworking.
What types of screws should you use in your projects?
For woodworking you can narrow it down to just a few choices. Here are my bottom line recommendations; the best screws for woodworkers.
- I highly recommend using premium or multi-purpose screws, such as Spax, GRK or Hillman.
- Get flat headed screws, the ones with the tapered heads for countersinking.
- If you can, use square or star drives. They work better and will save you a lot of frustration.
- The most common screws I use and like to keep on hand at all times in my shop are #8 1-¼" star head screws.
These are the most commonly used wood screws in my shop.
Why use screws?
I want to point out that I don't really use a lot of screws in woodworking. Usually I use wood glue, which is stronger and leaves no visible fasteners. The downsides to glue are that you have to wait for it to dry and once you've assembled something, you can't take it apart.
I often use screws for shop projects and jigs. With these, I'm not concerned about the appearance as much and love the time-savings screws give me.
Screws are also used to hold things together where expansion and contraction of the wood can be an issue. A common use is to attach a tabletop to a base. The screws will be set into a slot, allowing the wood to move as humidity changes.
For some projects that are sort of in the middle ground between making an heirloom dresser and a workbench, I like to use pocket screws. They are great for making cabinets and other casework. They make assembling these types of projects, say a bedframe, much easier and quicker. And of course, you want to position the pocket holes on the undersides or back of projects where they won't be visible. Learn the basics of pocket hole joinery.
What's the difference between a screw and a bolt?
There is no agreement on this, but personally, I view a bolt as a fastener that goes all the way through two material with a nut attached, while a screw pulls two pieces together and only the head of the fastener is visible. But I can think of plenty of exceptions such a machine screws.
Are Nails Used in Woodworking?
There is a common misconception among non-woodworkers that we use a lot of nails. Nothing could be further from the truth. In the ten years of projects on this channel, I don't think I have ever used nails in a project, other than for decorative purposes. Sometimes I use brads for holding boards together while glue dries, but never as a sole means of assembly.
Nails are a pain to hammer in, can bend, and you can easily mar the surface of your project with the hammer head. Not only that, but they don't hold nearly as well as screws and can work themselves loose.
Parts of a Screw
A screw is made up of 4 components:
- The tip
- The shank
- The threads
- The head
The Tip
Screws used in woodworking will have a pointed tip to help guide the screw into a precise location. Self-drilling screws have a split point that cuts into the wood like a drill bit. Other screws, such as machine screws have no point.
The Shank and the Threads
The treads of a screw wrap around the shank. Together, this is the part that drives into the material. The threaded part of some screws stops before it gets to the head, while other screws are fully threaded.
Shanks and threads come in different sizes. The diameter is indicated by a number. The most common wood screws are number 6, 8, and 10, the larger the number the bigger the thickness. I almost always use #8 diameter screws. Longer screws are usually #10s.
In the U.S. threads are sometimes indicated in threads per inch, usually 24 or 32 tpi. These are important to know with machine screws or bolts where you need to get a nut to match. Sometimes wood screws come in coarse or fine threads. Use fine threads for hardwoods and coarse threads for softwoods and plywood.
So when you are reading a box, the first number will tell you the screw diameter. This will sometimes be followed by the threads-per-inch, then then length of the screw.
The Head
There are two components of a screw head. It's head shape and It's drive type. Read on to learn about these.
Types of Drives
There are lots and lots of different types of drives, but thankfully, there are just a few common ones you need to know.
Slotted: What is a Flathead Screw?
Slotted screws are the original method for driving a screw. Like the name implies, it's just a slot that a flathead screwdriver turns. For this reason, these types of screws are commonly called flathead screws way more often than slotted screws.
Flathead screws require a lot of patience to use and are very difficult to drive with a drill or impact driver. It's weird how common they still are, still readily available at hardware stores. Basically they suck and I would never recommend them for woodworking with one exception: if you want to make a period piece of furniture with historic accuracy. Other than that, avoid slotted screws whenever possible.
Phillips
When Phillips screws came out in the 1930s, they were a vast improvement over slotted screws. A Phillips head driver will stay in place a lot better, but they still have an annoying tendency to cam-out, or slip when driving the last bit into wood. This can ruin the head and also ruins the driver.I have heard that they were designed to do this in order to prevent over tightening, but I'm not sure if that's true.
They come in different sizes so always make sure your driver matches and fits well. I really wish Phillips screws would become obsolete, but they are still extremely common in the U.S. the vast majority of screws sold at hardware stores are still Phillips.
Square (Robertson) Drives
Square drives are a huge improvement! They are also called Robertson screws and are most common in Canada. They are definitely harder to find in the U.S. Their square shape greatly reduces, almost eliminating cam-out and driver slipping. Here in the U.S. you will mostly find these in pocket screws.
Star (Torx) Drive
Star drive screws are becoming more and more common in the U.S. and are my absolute favorite type of drive. The star shape virtually eliminates cam-out and the driver almost never slips out. Plus they can accommodate a lot of torque. Usually they are sold on premium quality screws that won't snap if tightened too much. And when you buy a box, it usually comes with the driver tip you need.
Head Shapes
Like the drive types, there are all kinds of head shapes. Luckily, there are really only two that common in woodworking.
Flathead
This is where the terminology can get a little confusing. It's easy to confuse a screw with a flad head, and a slotted screw that we often call flathead screws. For woodworking a flathead screw is the most common kind of screw to use. It has a beveled head that seats neatly into the wood, making it flush with the surface
You can just power the screw into the wood to make it flush, but you will get better and cleaner results if you use a countersink bit to drill a pilot hole, or use a countersink to cut the bevels after you drill a pilot hole.
Panhead of Rounded
Panhead or roundheads can have shallow or deep domes. They sit on top of the wood and aren't used much for woodworking. You will need to use these when attaching some other material to wood…something that you can't countersink, say metal or plastic.
Types of Screws
Standard Wood Screws
Wood screws are widely available in all home centers and hardware stores and are designed to join two pieces of wood together. They are threaded part of the way and then have a smooth shank at the top. This helps hold the screws in place. They are relatively inexpensive and come an all kinds of diameters and head shapes. You will usually want to use the ones with the tapered heads. Unfortunately, in the U.S., most woodscrews are still only available with Phillips heads instead of star or square drives.
Drywall Screws
A lot of woodworkers use drywall screws, mostly for shop projects and jigs. They are inexpensive, usually cheaper than wood screws and easy to find just about anywhere. They have thinner shanks than wood screws, usually about equal to a #6 screw and threads that run the entire length of the screw. Because of their thinness they are really brittle. Especially ff you are drilling into hardwood, they are really prone to snapping, but I've had this frustrating experience with using them for 2x4s too. Like wood screws, in the U.S. the heads are almost always Phillips. Also, the heads have a bugle shape to reduce tearing the paper on drywall. They don't match the beveled shape of a countersink. In general, I don't recommend using drywall screws for woodworking projects.
What's the difference between a drywall screw and a wood screw?
Multi-purpose (production) screws
Production or Multi-purpose screws are my absolute favorite types of screws. Common brands include Spax or GRK. These screws are made with hardened steel and are incredibly strong. I don't think I've ever had any break. They have self-drilling points that eliminate the need for a pilot hole, but I would still pre-drill for critical pieces. Especially near the ends of boards to prevent splitting.
The best part is that they come in star or square drives so your driver stays in place and won't slip out like with Phillips. Plus, when you buy a box, it comes with a driver bit. There is really only a single drawback to using these: they are expensive. Maybe twice as much as regular wood screws. And while my Mere Mortals philosophy is always to be frugal, this is one instance where I believe it's worth spending the extra money. The amount of time and frustration these types of screws save is enormous.
If you've never used multi-purpose or Spax screws, just get one box and try them out. I guarantee, you will wonder why you didn't try them sooner!
Other Types of Screws
Deck Screws
If you are building outdoor projects, use deck screws. They are made of hardened steel and have a corrosion resistant coating.
Stainless Steel Screw
For even better corrosion resistance, especially on boats and in salty marine environments, you can use stainless steel screws. While they offer the best protection from the weather, they are not as strong as deck screws and are very expensive.
Pocket Screw
Pocket screws are self drilling and have a wide head that grabs the flat shoulder made by drilling pocket holes. If you use regular wood screws with pocket holes, they may drive all the way through, or possibly split the wood. I use the Kreg pocket screws, but you might be able to substitute pan head screws. The Kreg screws have a square drive which makes them really easy to seat. Watch my pocket hole basics video to learn a lot more about pocket hole joinery.
Machine Screws
Machine screws have no points and are intended to use in holes that are already tapped or with a nut. They are threaded along the entire shaft are sold in threads per inch. When you buy them, make sure the nuts' threads match. You may occasionally need machine screws to fasten a couple boards together, but they aren't common in woodworking.
Sheet Metal Screw
Usually, sheet metal screws are tiny with a sharp point intended for piercing and driving into sheet metal. Think of heating ducts for instance. They usually have pan heads and will probably work as a wood screw if you need a substitute.
And there's a basic look at the various types of screws. While there are a lot of choices available, there are only a few different types of screws a woodworker will ever need. Know what kind you need for your project before going to the hardware store or home center. Just buy what you need. I don't recommend stocking up on anything other than #8 1-¼" screws. I always like to have these on hand.
What Is the Diameter of a Number 8 Wood Screw
Source: https://woodworkingformeremortals.com/types-screws-use-woodworking-basics/
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