It behooves any homeowner or do-it-yourself enthusiast to learn the difference between different types of screws. Wood screws, drywall screws, and machine screws all look a little bit different, and serve different purposes. Read our guide below on how to decode screws before your next home improvement project to streamline your repair work and make renovations a breeze.
Types of Screws and Their Uses
When it comes to screws, one size doesn’t fit all. Different materials and applications require specific types of screws for lasting holds. Below are some of the most common screw types and their respective uses.
Wood Screws
Homeowners should use wood screws in wood and wood-based materials, either inside or outdoors. These steel screws feature a coarse thread that bites into wood fibers, which provides a strong hold. They also have a tapered design that makes driving easier. They’re available in various lengths and diameters.
You can use specialty wood screws for more specific tasks. Decking screws are designed to resist corrosion in outdoor projects, for example, while cabinet screws are designed for attaching cabinets to walls.
Drywall Screws
Use drywall screws to hang drywall panels. You shouldn’t use them for other projects because they are brittle. Use screws with fine threads for metal studs, and coarse threads for wood studs.
Machine Screws
Machine screws have a uniform diameter and feature fine threading along their lengths. You should use them with nuts or in pre-tapped holes, and as part of metal-to-metal connections that are common in machinery or appliances. Machine screws are available in various head styles and thread pitches.
Screw Head Types
Read about several common screw head types below.
Flathead
Flathead screws feature conical heads that sit flush against surfaces. These are the best screws to use when you want a smooth surface. Remember that they can be difficult to remove once they’re fully seated.
Phillips Head
Phillips head screws feature cross-shaped recesses that offer more torque on the screw. They’re less likely to slip than slotted screws, but they can be prone to stripping if you tighten them too much.
Torx (Star) Head
Torx or star-shaped screw heads feature superior grip, and are especially resistant to stripping. They also let you put a lot of torque on the screw. Remember that you’ll need a specific Torx driver for installation and removal.
Other Head Types
Below are two more specialized screw head types:
- Hex Head: Hex head screws require a wrench or socket for installation, and are suitable for heavy-duty applications.
- Square Head: These provide a secure fit and are less likely to strip than Phillips or slotted screws.
Decoding Screw Sizes
You must understand the differences between different screw sizes to select the correct model for your project. Read about the numbering systems for screws below.
Diameter
The “#” symbol represents the diameter of the screw. Higher numbers indicate larger diameters, and larger screws may use fractional inch measurements. Common sizes for wood screws range from #4 to #14.
Length
You can find the screw length metric after the diameter, and it’s usually measured in inches. A #10 x 2″ screw has a #10 diameter and is 2 inches long, for example. Look for a length that holds well but doesn’t poke through your project. You can determine the appropriate length by taking the thickness of the material you’re attaching and multiplying it by 2.5. For example, if you’re hanging a piece of 1/2-inch drywall, look for a screw that’s one and a quarter inches long.
Thread Count
Thread count refers to the number of threads per inch in the screw, and affects the screw’s grip. A “coarse” label means there are fewer threads per inch in the screw. This is ideal for soft materials such as wood. Fine means there are more threads per inch, and this is best for harder materials such as metal.
Indoor vs. Outdoor Screws
Choose the screw that works best for either your indoor or outdoor project by following the advice below.
Indoor Screws
Indoor screws are typically made of steel, and feature a basic finish that’s not designed to withstand moisture or harsh conditions. Below are two common varieties:
- Black phosphate-coated drywall screws are for interior use only.
- Zinc-plated screws are suitable for most indoor applications.
Outdoor Screws
Outdoor screws are designed to resist corrosion from moisture and exposure to harsh weather. There are several finishes that are suitable for outdoor use, including the following:
- Ceramic-coated screws
- Hot-dip galvanized screws
- Stainless steel screws
Always use screws that are specifically rated for pressure-treated wood when you’re working with this material. These screws are designed to resist corrosion from the chemicals that are common in the lumber treatment process.
Specialty Outdoor Screws
Below are specialty outdoor screws that are suitable for more specific applications:
- Deck Screws: These are coated to resist corrosion, and frequently feature a self-countersinking head to reduce splitting.
- Landscape Timbers Screws: These screws have superior holding power and can handle heavy loads and outdoor conditions.
Tools for Identifying Screws
Read below for tips on how to match or identify an existing screw.
Screw Gauges
A screw gauge features holes of various diameters that can help you determine screw size. It also features a ruler that can help you to determine length. You can purchase one at most hardware stores.
Using a Screw Gauge
Follow the steps below to use a screw gauge:
- Insert the screw into a hole until you find a snug fit.
- Read the number next to the hole to determine the screw size.
- Use the ruler portion of the gauge to measure the screw length.
Digital Calipers
Digital calipers can measure the diameter, length, and thread pitch of a screw precisely. These tools are available in electronic and manual versions, and offer digital readouts for easy reading.
Choosing the Right Screw Drill Bits
The drill bit you choose for your screws is just as important as the screws you choose. Different screw types require different drill bits:
- Countersink bits: Ideal for flathead screws, and allow the head to sit flush with the surface
- Pilot hole bits: Help prevent wood from splitting by creating a guide hole for the screw
- Torx bits: Necessary for Torx head screws
Be sure to match the drill bit to the screw size you’re using and the material you’re working with, such as wood, metal, or masonry.
