Screws are an indispensable construction tool for many projects, but using the wrong type and size can make your work more difficult. Incorrect fasteners can split wood, break nails and weaken a structure’s overall soundness. Knowing three essential measurements — screw gauge, length and threads per inch (TPI) — will help you find the right screws for your job.
The first number in a screw size indicates the screw’s diameter, also known as the “gauge.” This is used for screws with a head that sits above the material. It’s also the first measurement in screw sizes that use a metric system, which is indicated by the number of millimeters preceded by the letter M (e.g., M6 = 6 mm).
Measuring the screw’s threads is the next step in finding the correct screw size. The number of thread peaks in one inch of screw length is known as the thread pitch. For example, a screw with coarse threads has more peaks than a screw with fine threads.
The final step is determining the screw’s length, which will depend on the depth of the hole you’re going to drill or where the screw will be installed. The following table will help you choose the correct length for your project. In most cases, a screw’s length will be listed on the package or in the product description. If you’re unsure of the size of your hole or the length of your screw, consult this guide for more information on how to measure screw lengths and the conversion between imperial and metric screw sizes. pilot hole for 1/4 lag screw