Choosing the Right Screw For Your Woodworking Project

Finding the right screw for your woodworking project can be a challenge. Choosing a screw that’s the correct length, gauge and head-bore size is a critical step to ensure it will be properly driven into the material and hold it securely. Adding other factors such as the type of wood, lateral and sheer forces, pilot holes and threads can make selecting the right screw even more difficult.

Luckily, there are some general rules that can be followed to simplify the process. When a screw is labeled with the inch system, its diameter is indicated by its first number; the same goes for metric screws. For example, a screw with the size M6 has a diameter of 6 mm. A screw’s shaft, or shank, is also specified by its second number. The shaft is the part that runs from the head down to the end of the screw.

Screws with hex heads are typically used in construction and framing carpentry and come in a wide variety of sizes. These screws have a hexagonal shape that’s easy to grip using power tools and are often made of stainless steel for rust resistance and higher strength. Other types of hex head screws include the gutter screw, which is commonly seen in applications like gutter repair; the modified truss screw, which features a hex washer that adds additional bearing surface to support heavy loads and flanged trusses; the pan head, which is ideal for high-torque applications; and the rack screw, which is used in 19’’ racks to secure equipment.

The shank of a screw is also specified by its threads. The threads are the spiral shape around the screw’s shaft and are measured in threads per inch, or TPI. A lower TPI is coarse, while a higher TPI is fine. Screws with coarse threads are typically used in softwoods, while fine threads work best with metals and hardwoods.

Finally, the length of a screw is determined by how deep it will need to be driven into the material. Ideally, the screw should go through the thinner piece and thread into the thicker one, so it’s important to choose the right length.

When measuring a screw’s diameter and TPI, it’s easiest to use a caliper for accuracy. Measuring the thread pitch is slightly more challenging, as it involves determining the distance between two adjacent threads, which can be hard to see without a magnifying lens.

In addition to the above measurements, screws may be labeled with a tolerance class number, an LH symbol if they’re left-handed and a screw length. While you might be able to decipher these numbers by reading the screw’s callout on its box, it’s helpful to understand the basics of how to measure screw diameter and length for different projects. #10 screw diameter