Screws may not be the most glamorous of home improvement hardware, but they’re a crucial part of everything from wall framing and cabinetmaking to everyday projects like building wood benches. The screw aisle at your local hardware store is packed with an array of seemingly endless options, so it’s important to know how to identify the right fastener for the job at hand. For this, you’ll need to know the screw’s major thread diameter and shaft length. The most useful way to find this information is to look at a screw chart, which will have the screw’s gauge, threads per inch (TPI), and shaft length. Screw charts also usually specify the head size, which is determined by the thickness of the screw head.
Measuring the screw diameter is relatively easy. You can use a pair of calipers to get the measurement, or you can simply look at the number on the package. Screws are typically listed with the diameter and shaft length in both imperial and metric units. When they’re listed in imperial, the screw gauge and length are usually specified separately. When they’re listed in metric, the screw diameter is usually specified first and the shaft length is then indicated by a number following it, such as 5.0 x 60.
The screw shaft is the smooth area between the screw head and the thread. The shaft is normally made from a metal, such as steel or stainless steel. The type of metal can have a significant impact on the screw’s performance, with more corrosion-resistant options suitable for outdoor applications and construction projects. The screw’s overall appearance is also influenced by its coating, which can add an element of style or provide added protection against moisture and temperature change.
Depending on the type of material you’re using, you may need to drill a pilot hole into which the screw will be driven. This is especially true of hardwoods, which are prone to splitting. You can minimize the risk of splitting by drilling a pilot hole with a regular bit or a countersink bit before driving the screw.
Most screws are designed to be driven into boards across the grain rather than into the end grain. When you screw into the end of a board, you’ll need longer screws to ensure they penetrate enough wood to hold securely.
Screws are designed to penetrate into the material and gain strength by friction and the pressure of wood fibers gripping the threads. As such, a good rule of thumb is that your screw should be at least half as thick as the wood you’re screwing into. If you’re screwing into very thick material, then you might need to go even larger. #5 screw diameter