How to Choose the Right Wood Screw Size and Type

Wood screws have been in use for centuries, usually serving a simple but essential purpose: joining two pieces of wood together. Here, we’ll take a look at the different types and uses of wood screws, including how to properly size them for your needs.

Though wood screws are extremely common and can be used in a wide variety of applications, they’re most often used to join two or more pieces of wood together. Wood screws may also be used with some types of hardware or even with drywall.

Commonly found in many types of wooden furniture, wood screws can be used as great fasteners. They’re designed to create a strong joint and make an excellent alternative to nails and clamps when you’re working with wood.

In addition to their use in woodworking and furniture, some wood screws may also be used in outdoor applications, such as carpentry and constructing or repairing wooden decks. Compared to metal screws, wood screws have fewer threads and are not threaded throughout, with a shape that tapers from the head to the sharp, pointed end.

One more important note for the uninitiated: wood screws are used to join wood to wood, but they are never made of wood. In fact, most wood screws are made of steel.

Whether you’re shopping for wood screws or hoping to determine what type of wood screw you have on hand, the most common considerations are the material, drive type, head type or head shape, length, and gauge or thickness. See below for more detail on each of these qualities.

The most common wood screw materials are carbon steel and brass for indoor applications and stainless steel for outdoor use. Outdoor wood screws are frequently treated with a coating (by electroplating or galvanizing) to prevent corrosion and deterioration. Many manufacturers have developed their own proprietary coatings, most often for deck screws. Screws may also be coated with different finishes (e.g., bronze, nickel, or black oxide) for aesthetic or decorative reasons.

The most common drive types for wood screws are the everyday Phillips and slotted head styles, but many other types are available, including hex head, square head, Torx/star head, and Phillips square head screws.

For the most part, the head types or shapes of wood screws are either flat, round, or oval, but other options do exist.

• Flat head screws have a flat top and a conically shaped underside. This allows the wood screw to sit flush with the finished workpiece, creating a smooth surface.
• Oval head screws have the same conically shaped underside as flathead screws, but with a decorative top that protrudes slightly above the surface.
• Round head screws are flat on the underside of the head, with a domed top that sits above the surface of the workpiece.

The size of a wood screw is generally determined by its gauge (or thickness/diameter) and the length of its shaft. Both length and diameter may be measured in inches, but the gauge is a screw size number, which can be confusing if you haven’t encountered it before. For convenience, we’ve provided a table below that converts screw size or gauge into the screw’s diameter in inches.

Wood Screw Sizing Table

In the above chart, the column labeled “closest fractional size” relates to screw size (or gauge) and references the closest fractional diameter of the corresponding screw shaft. The other two columns are designed to help you determine which drill bit to use when drilling a pilot hole for that screw size, with options for both hard and soft woods.

When it comes to choosing the right length for your wood screws, remember that longer screws will create a stronger joint—but screws must not be too long or they’ll break through the opposite side. Similarly, a thicker screw is stronger, but too much thickness can lead to splitting. When it comes to choosing the right wood screws, you may also want to consider the type of wood you’re using and whether you plan to drill a pilot hole first.

Pocket hole screws are commonly used when building furniture or cabinets. When selecting a pocket hole screw, be sure to choose screws with coarse threads for softer woods (such as pine) and fine thread screws for harder woods (such as maple or oak).

Wood screws have stood the test of time, and their versatility means they’re probably not going away anytime soon. No matter what your needs are, Zoro’s excellent selection of wood screws can help you realize your woodworking dreams. While you’re shopping, don’t forget to check out our full selection of useful fasteners.

The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.