Choosing the correct wood screw size, length, and gauge for your next project can be challenging. There are many factors to consider, including the thickness of the wood, the type of screw head and shank, the lateral and sheer forces applied, and whether or not pilot holes should be used. Fortunately, there are some general guidelines to follow that can help you select the right screw for any job.
The first thing to note is that there are two different screw sizes, the head diameter (gauge) and the shank diameter. The size of the screw is indicated by the number that is printed on the head of the screw, and the shank diameter is shown by the letter that is printed on the body of the screw, following the head diameter. For example, a #10 screw has a diameter of 3/16 inch and a shank diameter of 5/32 inch.
In addition to the screw size, you will also see a letter or symbol that indicates the tolerance class, which refers to how tightly the screws fit together. There are five tolerance classes, ranging from class 1 to class 5. The class is determined by how much the head and shank diameters differ. The smaller the difference, the lower the tolerance class.
If you have a tolerance class of 1, the screws will fit each other very closely and have little to no play. Class 5 screws, on the other hand, have a lot of play between each other. In addition, you will likely see a letter or symbol that indicates that the screw is left-handed. Left-handed screws are threaded in reverse, which means they will fit tighter into the holes they are going into than right-handed screws.
Finally, you will also see a type of screw material and coating listed. The coating protects the screw from corrosion and moisture, which can rust or damage the screw. Screws are available in a wide variety of materials and finishes, from galvanized steel to silicon-coated bronze. The type of screw that you choose will depend on the application and your budget.
When using screws for wood construction, it is important to remember that the length of the screw must be sufficient to provide a firm grip on the wood. This can be achieved by drilling a pilot hole in the wood before driving the screw. A pilot hole should be drilled using a bit that is slightly larger than the screw diameter, to prevent the wood from splitting around the fastener.
A pilot hole is especially important when working with hardwoods, such as oak and walnut, because these types of wood are prone to splitting. However, it is a good idea to drill a pilot hole in softwoods as well. Pilot holes also reduce the friction and pressure of the wood fibers gripping the screw threads, which can loosen over time. This may result in the screw coming undone over time. For these reasons, it is recommended that you use a countersink drill bit when drilling pilot holes in wood. #12 screw diameter