Screw Sizes – How to Choose the Right Size

Screws are an incredibly useful tool for all sorts of construction tasks. But choosing the right screw size can be tricky — if you pick a wrong one, it can split wood or even affect the structural integrity of a building. In this article, we’ll explore three essential screw measurements: gauge, length and threads per inch (TPI).

The first number on a screw is its gauge, which refers to the screw’s overall diameter or major diameter. For example, a #0 screw has a smaller diameter than a #2 screw, and a #4 screw has a larger diameter than a #3 screw. Screw gauges are usually labeled in fractions of an inch. You can use a screw gauge guide to find out what a specific screw gauge corresponds to in decimal form. Engineering Toolbox has an easy-to-use chart for that purpose.

When it comes to choosing the length of a screw, the general rule is that a fastener should be at least half as long as the thickness of the material it’s being installed into. That’s why screws are typically sold in packages with a length indication, such as “10 x 2.”

Finally, the last number on a screw is its thread count. Screws have threads that run up the shaft of the screw, and they can be coarsely or finely spaced to suit your application. For instance, some wood screws feature threads with tiny serrations that help prevent splitting of the wood when driving them in. 1/4 lag screw pilot hole

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