Choosing the right screw size is essential to ensure that your work stays safe and secure. It’s also necessary to avoid screw thread damage, which can be costly.
Fortunately, there are many helpful tools available to make this process as easy and accurate as possible. These include gauges and screw length measurements, which are used to determine the diameter of a thread and its shaft. Using these measurements, you can quickly and accurately select the right fastener for each job.
For example, when purchasing wood screws, you can find the head size (B) and threads per inch (TPI) on the packaging. This information is necessary to know before starting your project, as each screw type has a specific threading and length. For instance, a #6 wood screw has a major diameter of 1/4″ and a TPI of 32, so it is classified as a standard “wood” screw.
The crest of a thread is the surface that connects the root and base. The helix angle is the angle included in the conical spiral of a thread, resulting from the pitch and lead. A helix angle, in turn, defines the distance between adjacent crests, or peaks, of a thread.
The pitch diameter of a thread is the diameter of a cylindrical surface, axially concentric to the thread, that intersects the flanks of the thread at equidistant points. This line, known as the “pitch diameter” (PD) or “pitch diameter line,” cuts through a sharp-V form of the thread at exactly half its pitch distance. #8 screw diameter
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