Wood Screws: A Simple Guide for Beginners
Standing in the aisle of wood screws can definitely be intimidating. Let’s talk about the different types of wood screws and how to pick the perfect one for your project.
Wood Screws are the main type of fasteners used in woodworking and can be used to join lumber, plywood, or MDF. However, there are many different types of wood screws available that can be overwhelming and confusing.
I remember going to The Home Depot when I was first starting out. The wall of screws was overwhelming and intimidating, to say the least. There were so many options, sizes, and numbers to understand and pick from. And I had no idea what any of that signified.
Here is a simple and complete guide for what to look for in wood screws. I will also share the exact ones I use below.
Table of Contents
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The Parts of a Wood Screw
The key to understanding and picking the right screw for your project starts with understanding the exact function of each part of the wood screw.
Let’s break down each of these parts and their function starting from the bottom.
The Tip
The tip or the point of the screw is the part of the screw that first enters the wood. It is usually pointed in wood screws so they can puncture the wood and drive in. There can be two types of tips in wood screws.
- Self-drilling tips have a little notch cut into the threads of the screws – almost like a tiny drill bit. These screws can drill a hole as they are driven into the wood. Although they don’t need a starter hole in the wood, I highly recommend pre-drilling to avoid splitting.
- Regular tips are just regular screws with uniform thread all the way to the bottom.
There are also machine bolts that are sometimes used in joining boards. These have a flat bottom and go all the way through to the other side. Nuts and washers hold these in place.
The Threads
The threads are the spiral around the shank of the screw. When a screw is driven into the wood, these threads act as “teeth” and grab onto the wood fibers.
They come in different densities; generally, there are coarse and fine threads.
- Coarse thread screws have a thread that is wider apart and is used for softwoods like pine, birch, etc, and plywood.
- Fine thread screws have a thread that is closer together and are used for hardwoods like walnut, maple, etc.
The Shank
The shank is the main body of the screw that holds the thread. It is the length of the screw from the head to the tip. This is the most important part of the screw. Not only does it hold the thread, but it also plays an important role in the strength of the joint.
The thicker the shank, the more stress the screwed joint can withstand.
Unthreaded shank
Good quality wood screws will have a small fraction of unthreaded shank between the head and the thread.
This unthreaded shank plays an essential role in how well the wood screw works in pulling the two boards being attached together.
When you are attaching two boards, the unthreaded shank will sit in the first board, causing compression from the head to the threads as the screw is driven in. This causes the two boards to pull together and create a tight joint.
If there were no unthreaded shank, aka threads all the way from the head to the tip, the screw would keep driving through both the boards without pulling the boards together.
Many good-quality screws also have a knurled shoulder following the unthreaded shank before the thread. This enlarges the screw hole for the non-threaded portion of the screw. This, in turn allows the wood to settle easily and increase the drawing strength.
Important – when pre-drilling the hole for a screw, always use the diameter of the shank. This will give the threads wood to grab onto around the predrilled hole.
The Head Shape
The head of the screw holds the drive (where you will add the driver bit to turn the screw). Heads come in a variety of shapes and sizes, depending on the specific application.
In general, they can be split into two types –
- Countersinking screw heads – the screw head goes below the surface of the wood and can be hidden with wood filler if needed.
- Non-countersinking screw heads – the screw head sits at the top of the wood surface and is visible.
The most common types of screw heads are:
Flat head or bugle head
Also known as countersunk heads, flat head or bugle head screws have a flat top and a conical head. They are used where the screw head needs to sit flush with or below the surface of the wood.
Good quality wood screws also feature cutting nibs on the bugle head, which help with countersinking.
| Pros | It provides a smooth, finished appearance, ideal for surfaces that will be visible or touched. |
| Cons | Requires predrilling a countersinking hole, or need a good quality counutersinking head with cutting nibs. |
Trim head
Trim head screws have a smaller head compared to traditional screw heads – just a little bit larger than finish nails. This makes them less visible when installed, making for a cleaner finish. Even though the head is slightly larger than finish nails, its holding power is higher than finish nails.
| Pros | They are usually self-drilling and can easily be hidden in projects. These are also a great alternative if you do not have a nail gun but would like to build a quick project using just a power drill. |
| Cons | They can be expensive They should not be used for joints that undergo heavy stresses. |
Round or pan head
Round head screws are rounded on the top and have a flat underside. These are commonly used to attach other materials, such as metal or plexiglass, to wood or in projects where the head can protrude above the surface.
| Pros | – The underside sits flush with the surface and has a high tightening torque due to its design. – Since it is above the surface, it can be easily removed. |
| Cons | Not great for applications where you need to hide the screw. |
Washer head
Washer head screws are round head screws with a washer attached to the bottom of the head which provides a larger surface for contact than regular round head screws.
They are most commonly used in pocket hole joinery. The washer acts as a stop at the end of the pocket hole and helps pull the two boards together for a tight fit.
Another application is cabinet screws which are used to mount cabinets to the wall. The washer head sits flush with increased holding power.
| Pros | The wider head distributes pressure over a larger area, resulting in strong holding power and reducing the risk of pulling through the material. |
| Cons | – These are usually expensive compared to regular round-head screws. – They are visible above the surface, although they can be countersunk using a predrilled hole. |
These have quickly become my favorite way to attach boards together over pan-head or round-head wood screws using the Kreg Quick Flip, which predrills a counterbore to fit the washer-head perfectly. Plus, since I build a lot of projects with pocket holes, I always have them on hand.
The Drive Type
The drive of the screw is the type or shape of the hole at the top of the screw head where a bit fits in and helps install the screw.
In general, there are a LOT of different shapes for drive types. The most common types of wood screw drives are:
Flathead or slotted
The flathead, or slotted, drive has a single slot in the fastener head and is driven with a flat-bladed screwdriver. This is the oldest type of screw drive and is still widely available. Unfortunately, this is the worst design for a screw.
| Cons | It is impossible to tighten it with a power drill. The bit will simply spin out. The only way to tighten these are using a screwdriver, but that doesn’t work for build wood projects. |
Phillips head
The Phillips head drive is a cross-shaped slot in the head. These are incredibly common in wood screws. These are a huge improvement from flathead screws and allows for more torque to be applied compared to flathead screws without slipping.
| Pros | – Better torque: Allows for more torque to be applied compared to flathead screws without slipping. – Self-centering: The cross shape helps to center the screwdriver for easier driving. |
| Cons | Cam-out: The design allows the driver to cam out (slip out) under excessive torque to prevent over-tightening, but this damages the screw and also the driver bit. |
What is cam out? When the driver bit slips out under excessive torque. This ends up stripping the screw head.
Square (Robertson)
The square, or Robertson, drive has a square-shaped slot and is driven with a square-tipped driver bit. This is most commonly found in pocket hole screws.
| Pros | High torque capability: Provides a good grip between the screw and the driver, allowing for higher torque application without slipping. Reduced cam-out: The design significantly reduces the risk of the driver camming out of the screw head. |
| Cons | It is not as widely available as Phillips or flathead drives in some regions. It requires a square-drive screwdriver or a bit |
Star drive (Torx)
The star drive, or Torx, screw has a six-pointed star-shaped pattern and requires a Torx screwdriver or bit. It is my screw type of choice.
| Pros | – Superior torque transmission: The design allows for higher torque application with less risk of cam-out compared to Phillips or flathead screws. – Longer tool life: The precise fit between the screw and the driver reduces wear on both. – Increased driving stability: The star shape provides excellent engagement between the screw and the driver, making it suitable for precision work. |
| Cons | Specialized bit required. It can sometimes be found in the package with the screws. Torx screws and drivers can be more expensive due to their specialized design. |
One of the key things to remember when driving screws into the wood is to have the drill/driver on the correct setting so the screws do not get stripped or stuck. Read more about how to use a drill and the drill/driver settings.
Wood Screw Materials
Wood screws are available in a variety of materials. The material you choose for the screw will depend on the application – indoor vs outdoor, how much stress the joints will see, etc.
The most common wood screw materials are:
- Steel: Steel is the most common material for wood screws and is available in many sizes. They are cost-effective and strong. These are recommended for indoor projects only as they can get corroded easily.
- Stainless steel: Stainless steel has long-term protection against corrosion and can be used for outdoor projects. These screws are more expensive than the steel screws.
- Coated Screws: Steel and stainless steel are often further coated to enhance corrosion resistance.
For example, zinc-plated steel screws are a great option for indoor applications because zinc corrodes 30% slower than steel.
There may also be an epoxy coating like in Blu-kote screws or a special coating in the RSS Rugged Structural screws to make them extremely rugged in outdoor conditions.
Wood Screw Sizes
Wood screw sizes are categorized by two main dimensions: gauge (diameter) and length.
Gauge (Diameter)
The gauge of a wood screw refers to the diameter of the screw’s body. It’s a number that typically ranges from #0 (very small) to #24 (large), though the most commonly used sizes in woodworking are between #6 and #12.
The higher the gauge number, the thicker the screw. The gauge number correlates to the size of the screw’s shank and, indirectly, to the size of the pilot hole needed.
Length
The length of a wood screw is measured from the tip to the underside of the head. This measurement determines how deep the screw can penetrate the joining materials. Wood screws can range in length from 1/4 inch (very short) to several inches long, depending on the application. The correct length of the screw is important to ensure that it can hold the pieces of wood together strongly without poking through the opposite side.
Common Wood Screw Sizes
- #6, #8, and #10 Screws: These sizes are versatile and widely used for a variety of general woodworking projects.
- #12 and Larger Screws: Typically used for heavier-duty applications where more strength is required, such as in deck building or framing.
Selecting the Right Size
When selecting a screw size, consider both the thickness of the materials being joined and the type of joint. A good rule of thumb is that the screw should penetrate at least half the thickness of the bottom material to ensure a strong hold.
For example, if you’re joining two 1/2-inch thick boards, you’d want a screw that’s long enough to go through the first board and at least 1/4 inch into the second.
My Wood Screw Recommendations
When you are looking to get a good quality wood screw, you want to ensure that the screws have all of the below properties.
- A partially unthreaded shank
- A knurled shoulder
- A Bugle head with cutting nibs
- A self-drilling tip
- A star drive
- Finish appropriate for indoor or outdoor use as needed.
Some of the brands/screws I use and recommend are:
These screws are a little on the expensive side but are totally worth the price. Good quality screws are definitely worth the splurge because you want them to last for a long time to come.
If you would like to look for budget-friendly options, you can get screws with all of the above features but with a Phillips head instead of the star drive.
I hope this article has given you the confidence to go out and pick the right wood screw for your projects.
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Anika's goal is to inspire and empower beginners with woodworking, DIY, home improvement, and home decor ideas.
She wants everyone to unlock their creative potential and experience the feeling that comes with making something. Nothing feels better better than seeing something and saying "I can make that!"
Excellent writeup. Timing couldnt be better and much needed as there is nothing like this anywhere. Your explanation is simple and easy to understand. I look at a lot of your videos for when I am stuck on my project. Keep posting more!
Thanks for this wonderful guide to screws!