Screws come in a wide variety of shapes, head-sizes and lengths to accommodate woodworking projects. The proper size of a screw for a particular application depends on the material, its thickness and the weight it will support. Choosing the right screw is essential to avoid splitting wood and compromising the strength of the project.
There are three key measurement considerations for screw sizes: gauge, thread per inch (TPI) and length. A good general rule of thumb is that a screw should enter the material at least half its own diameter. This may vary depending on the materials being attached, however. For example, thicker materials will require longer screws for a secure hold; while thinner materials may be best served with shorter fasteners.
Threaded screws are categorized by their major diameter and pitch, which is the distance from one thread’s crest to the next. Pitch and TPI are inversely related to each other, much like period and frequency in a wave. Coarse threads have larger pitches, while fine threads have smaller pitches.
When determining the screw size you need for a particular project, it is important to consider the type of material being used as well as the strength requirements and appearance of the finished product. Screws are also available in a variety of styles, such as hex, square and torque heads to suit power drills, flatheads and Phillips screws for manual screwing, and truss, round and button heads for woodworking applications. The size of a screw is usually listed in the package and includes the diameter, length and threading information. 5/8 to mm