Screws buying guide
Screws buying guide
Introduction
This screws buying guide explains what screws are used for, how they work, and how to choose the right type. It then looks at the different types in detail and the safety equipment you need when using them. Finally, it highlights some key things to consider before buying and answers some frequently asked questions.
What are Screws Mainly Used For?
Screws are mainly used to hold two or more pieces of material or objects together. For example, to join pieces of wood, fix plasterboard to wooden battens, secure a picture or curtain pole to a wall or attach hinges to doors. And they can be used for DIY projects and professional use.
How do Screws Work
Screws work by holding materials together. To do this, the screw’s head, which acts as a lever, is turned using a screwdriver or drill compatible with the type of screw head. This rotational motion or force is converted into a strong forward or linear force that, with the help of a spiral thread, drives the point of the screw into the material.
How to Choose the Right Type of Screw
All screws are made up of four main parts:
- Head: which has slots in the top to fit a compatible screwdriver/drill bit.
- Shank: the straight part of the screw which connects the head and thread.
- Thread: the spiral grooves which run down the length of the screw.
- Point: the end of the screw that’s first driven into the material when a rotational force is applied.
A huge selection is available for a wide range of applications. They can be classified by the type of material they’re made from, such as brass, stainless steel, carbon steel, etc., their size (diameter and length) and the different screw head types, drive types and thread types.
The screws you choose will depend on the task. Things to consider are the thickness, density, and strength of the substrate material, the size and weight of the load they need to hold, and the risk of the material tearing or splitting.
For example, the length should be long enough to securely hold the materials together but not so long that it passes through the other side. They should be thick enough not to be bent out of shape by hard materials but not so thick that they will split delicate materials.
Drive types
Screw head drive types refer to the shape of the slots in the screw’s head. There are many screw drive types available. Here are some of the most common:
- Slotted heads have a single groove across the diameter of the head.
- Phillips heads have a deep cross-shaped slot.
- PZ (pozidriv) heads have a deep cross-shaped slot and radial indentations set at 45º to the main cross.
- Torx (T or TX) heads have a star-shaped slot.
- Spider drive heads have a circular slot with 8 points of contact.
- Square heads have a square-shaped slot.
Each type of screw head must be turned using a compatible screwdriver or drill bit. Slotted drives are the most common, but they don’t provide much torque compared to the other types. Generally, the best screw head types have multiple contact points with the screwdriver/drill bit, as they provide more torque.
Screw head types
There are many different screw head types available to suit different purposes. For example,
- Countersunk heads sit below the material's surface, allowing a flush finish.
- Double self-countersunk heads are an improved version of the countersunk heads. They have small ribs on the countersink to assist with countersinking and give additional head strength.
- Flat heads sit flush with the surface of the material.
- Rounded heads (also called dome or button heads) sit above the material. These heads are often used in carpentry, where there is less chance of the screw head countersinking into the wood.
- Small screw heads are designed to be easier to conceal
What are Screw Gauges?
Screw gauge refers to the diameter of the shank on a screw. It's measured using an imperial system that ranks the size with a number from 1 to 20. The higher the gauge, the bigger the screw.
The table below shows how imperial gauge sizes relate to metric screw sizes and gives the clearance and pilot hole sizes needed for each gauge size:
|
GAUGE |
CLEARANCE HOLE |
PILOT HOLE | |
|---|---|---|---|
|
Imperial |
Metric | ||
|
2 |
2mm |
2.5mm |
1.6mm |
|
3 |
2.5mm |
3mm |
1.6mm |
|
4 |
3mm |
3.5mm |
2mm |
|
6 |
3.5mm |
4mm |
2mm |
|
8 |
4mm |
5mm |
2.5mm |
|
10 |
5mm |
5.75mm |
3.5mm |
|
12 |
5.5mm |
6.5mm |
3.5mm |
|
14 |
6.5mm |
6.5mm |
4mm |
Types of Screw
In this section, we list the popular types that can be used for various jobs and materials for professionals and DIYers.
Woodscrews explained
Woodscrews are designed to join two pieces of wood, such as hardwood, softwood, MDF, and chipboard. They feature a large sharp point to enable them to dig into wood easily and a tapered shank. They're available in different lengths and gauge sizes to suit different thicknesses and densities of wood. PZ and Torx drive heads are the most popular types, but they come in various other drive types too. Woodscrew head types include countersunk, double self-countersunk, flat and rounded.
Materials and sizes they’re available in:
Woodscrews are available in a range of materials such as carbon steel, hardened steel, zinc, stainless steel and solid brass. Brass is usually chosen for its appearance when combined with brass ironmongery such as hinges and door handles. Stainless steel is ideal for areas exposed to moisture, and carbon and hardened steel can be fitted without needing pre-drilled holes. In addition, all wood screw materials have high levels of corrosion resistance. They are available in gauge sizes ranging from 3 to 8mm and lengths from 12 to 300mm.
Top things to consider:
- Look for features such as shanks that reduce wood split, twin threads for a fast and accurate drive, and tips that don’t require pre-drilling.
- When choosing the thread, consider the density of the wood. It’s best to use fine threads for hardwoods and coarse threads for softwoods.
- For outdoor applications, ensure you choose those suitable for outdoor use.
Decking screws explained
Decking screws are specifically designed to join deck boards to decking joists. They have a braking fin on the thread, just under the screw head, that locks the screw in place, making the joint more secure than standard woodscrews. Decking screws come in various colours to match different deck board shades. Deck screw head types include countersunk, double self-countersunk, flange, pan, wafer, cylindrical, flat, and mushroom.
Materials and sizes they’re available in:
Decking screws are available in carbon steel, hardened steel, zinc, and stainless steel. These are all resistant to moisture and corrosion. And they're available in gauge sizes ranging from 3 to 6.7mm and lengths ranging from 16 to 200mm.
Top things to consider:
- Look for features such as slash tips to remove the need for pre-drilling and double threads for improved decking stability.
- When choosing the thread, consider the density of the wood. It’s best to use fine threads for hardwoods and coarse threads for softwoods.
Timber screws explained
Timber screws are specially designed for use on timber. They have an aggressive, coarse thread that grips wood securely into place. They come in various gauges, head and drive types, and sizes, meaning there is a choice of screw for any task.
Materials and sizes they’re available in:
These are available in carbon steel, hardened steel, zinc, and stainless steel. And, as they are most commonly used for outdoor applications, they often have a coating that protects them from the elements and stops rusting. They're available in gauge sizes ranging from 3 to 10mm and lengths ranging from 16 to 300mm. Timber screw head types include countersunk, double self-countersunk, flange, cylindrical, flat, socket, and wafer.
Top things to consider:
- When choosing the thread, consider the density of the timber. It’s best to use fine threads for hard timber and coarse threads for soft timber.
- Look for features such as a low friction coating for easy application.
Drywall screws explained
Drywall screws are used to attach plasterboard to light steel, wooden studs, or metal partitions. They’re typically lighter and have deeper threads than other types, enabling them to grip plasterboard securely and a sharp point so pre-drilling isn’t required. Types of screw heads for drywall screws include bugle, wafer, and countersunk. A bugle head sits flush with the plasterboard’s surface, a wafer head sits above the surface, and a countersunk head sits below the surface.
Materials and sizes they’re available in:
Made from steel or carbon steel, and either bright zinc-plated or with a black-phosphate coating. They're available in gauge sizes ranging from 3.5 to 4.8mm and lengths ranging from 13 to 100mm.
Top things to consider:
- Consider what material the plasterboard will be attached to, as different screws are suitable for different materials. For example, there are drywall to heavy steel screws, drywall to light steel screws, and drywall to wood screws.
Roofing screws explained
Roofing screws are designed for attaching sheet metal to steel or wood as well as for other general exterior construction tasks. But they can also be used on internal jobs. The flanged (or washered) type of heads have a built-in washer that’s designed to reduce vibrations and stop the screws from loosening. And there are self-drilling and timber varieties available.
Materials and sizes they’re available in:
Roofing screws are available in carbon steel and hardened steel. And, as they are most commonly used for outdoor applications, they have a coating that protects them from the elements and stops rusting. They’re available in gauge sizes ranging from 4 to 6.3mm and lengths ranging from 16 to 120mm.
Top things to consider:
- Consider the thickness of the metal sheet you are attaching, as each type is suitable for a specific thickness.
- If you are joining sheet metal to steel, choose self-drilling screws. But if you are joining sheet metal to wood, use timber roofing screws with a sharp point.
Self-tapping and drilling screws explained
Self-tapping screws are screws that create their own thread as they are driven into a material, ensuring a strong, tight fit. They are best used in soft materials such as softwoods and plastic. A pilot hole that’s slightly smaller in diameter needs to be pre-drilled before fitting.
Self-drilling screws, on the other hand, don’t require a pilot hole, as they pre-drill and fasten in one motion, making it easier and quicker to complete projects. They are suitable for attaching sheet metal to steel.
Self-drilling and self-tapping screw head types include button, countersunk, flange, pan, pancake, socket, and wafer.
Materials and sizes they’re available in:
Self-tapping and drilling screws are available in steel, carbon steel, and stainless steel. Gauge sizes range from 3.5 to 6.3mm, and lengths range from 12 to 120mm.
Top things to consider:
- Consider the material you are screwing into. Self-tapping screws are suitable for fixing sheet metal to softwood or plastic, and self-drilling screws are best for sheet metal to steel.
- Consider the thickness of the metal sheet you are attaching, as each screw is suitable for a specific thickness.
Masonry screws explained
Masonry screws (also called concrete screws) are self-tapping screws that are perfect for fixing materials directly into stone, masonry, and concrete without needing wall plugs. They have deep, wide threads, ensuring a secure fit once installed. Often used to fix timber, uPVC frames, pipes, and cable housing into masonry. The type of screw heads available for masonry screws include countersunk, double self-countersunk, flange, flat, pan, raised, and wafer.
Materials and sizes they’re available in:
Masonry screws are available in zinc, carbon steel, hardened steel, and high tensile steel. They have an anti-corrosive coating and are tarnish-resistant, making them suitable for outdoor use. They’re available in gauge sizes ranging from 3 to 10mm and lengths ranging from 16 to 200mm.
Top things to consider:
- When choosing masonry screws, consider the load it will bear, as different types are suitable for medium or heavy-duty loads.
Electrical screws explained
Electrical screws are designed for attaching electrical sockets, switches, and cable trunking to walls and metal. Their thread provides an ultra-strong fix because they are inserted right up to the head and will not work loose. Screw head types include raised and flat pan heads.
Materials and sizes they’re available in:
Commonly made from nickel-plated brass and stainless steel. Gauge sizes range from 3.5 to 5.5mm, and lengths range from 16 to 75mm.
Top things to consider:
- Look for self-drilling electrical screws for screwing into steel and flat pan heads to reduce the risk of overtightening.
Security screws explained
Security screws (also called tamper-proof screws) have special types of screw heads, which make them impossible to remove without specialist tools. They are a low-cost way of deterring thieves and vandals. Different head types include button heads and countersunk.
Materials and sizes they’re available in:
Made from stainless steel. Gauge sizes range from 4.2 to 8mm, and lengths range from 25 to 38mm.
Top things to consider:
- For applications where they will never need to be removed, choose one-way screws. This is because they can only be turned in one direction (to install them). Attempting to turn them the opposite way will cause cam-out (damage to the head). If they need to be removed in the future, choose two-way screws.
Hinge screws explained
Hinge screws are specifically designed to fit hinges. They have shanks that ensure a balanced and straight insertion which helps prevent them from snapping or working loose. They are available in various colours to match different shades of hinges. Types of screw heads for hinge screws include countersunk and pan.
Materials they’re typically made from, and sizes they’re available in:
Hinge screws are available in carbon steel or steel. Gauge sizes range from 3.5 to 5.5mm, and lengths range from 10.5 to 50mm.
Top things to consider:
- They can be chosen for their aesthetics as much as their practicality. Colours can be matched to the ironmongery you are fitting, as can their head shape.
- They have varying width threads depending on the material you’re screwing into, so always check yours are compatible.
- For outdoor applications (i.e., fitting gate latches and hinges), ensure you choose those that are suitable for outdoor use.
Flooring screws explained
Suitable for fixing a wide range of flooring, including softwood, hardwood, and fibreboard. They are specially designed to prevent floorboards from splitting. All flooring screws have countersunk heads.
Materials and sizes they’re available in:
Available in steel, carbon steel, hardened steel, and stainless steel. Gauge sizes range from 3.5 to 4.5mm, and lengths range from 25 to 75mm.
Top things to consider:
- Some flooring screws are designed to be used with specific types of flooring (i.e., tongue and groove, MDF, or solid wood), so always check you are buying those that are compatible with your floor type.
Other types of screws and accessories
Those listed above are the most popular types, but there are other more specialist and less popular screw types available, such as:
- Grub screws: work using a pinning action that pushes two surfaces against each other, negating the need for a nut. They are often used in applications requiring a small, unobtrusive screw.
- Carcass screws: have a thick shank and coarse thread, used to join chipboard.
- Chipboard screws: used for joining chipboard. This has a thread that extends right up to its head.
- Coach bolts (cup square bolts): these have a domed head with a square neck underneath, which locks securely into wood when they’re tightened.
- Coach screws: these are driven into materials using a spanner through a square or hexagonal head. They provide robust and heavy-duty fixing.
- Framework/PVC screws: self-tapping screws suitable for use with plastic.
- Connecting screws: these are made up of two parts: a screw and a hollow threaded rod that accommodates it. They are used to join objects such as door handles and locks.
- Screw caps and cups: these plastic covers are used for protective and decorative purposes. They click over the top of screw heads to leave a neat and finished look
Safety Equipment when working With Screws
Using hand and power tools to insert and remove screws comes with some risks, so it’s essential to consider how to protect yourself. For example, inserting screws into wood or masonry using a power drill may produce shooting debris and dust. So, consider wearing PPE such as goggles, gloves, and dust masks where necessary.
Key Considerations When Buying Screws
Here are a few other things to consider before buying:
-
What quantity is needed?
Screws are often sold singularly or in packs of varying quantities. Check how many you’ll need before you buy, as you can often save money by buying larger packs. And if you are a tradesperson who uses them frequently, buying trade packs of screws will save you money and time on repeat visits to the store. -
Do you need to remove existing screws first?
If you’re removing existing screws before fitting new, check the screw head type to ensure you have compatible tools. If they’re rusty and difficult to remove, try striking them on the head with a hammer to loosen the rust, then apply a lubricant such as WD-40. Leave that to work for a while, then try to remove it again. If the screw is at risk of stripping, re-cut notches into the head to give the screwdriver a better grip. And if that also fails, heat the screw with a blowtorch or something similar (as long as the surrounding material is non-flammable) and cool it quickly with water. This will cause the rust to crack away. -
What project are they needed for?
Before buying screws, consider the type of project you need them for. Although some are designed for multipurpose use, others are more specialised and are designed for specific applications. Using the right type for the job will ensure they can take the load and stay securely in place. - What material are they being used with?
It’s essential that the screws you use are compatible with the type of material you are screwing into, as using the wrong type can cause them to bend, break or work themselves loose. Using the right screws for the material will ensure they have a firm grip. Also, consider the thickness of the material as this dictates the gauge and length of screw required.