Whether you’re a new woodworker or have been doing this for years, you may not know the intricacies of screw sizes. Often, plans, instructions and other materials will reference specific kinds and sizes of screws that need to be used in projects. This can be confusing, especially when you’re shopping for the right screws and see a lot of different numbers listed (ie, #8 vs. #6 or whatever). This article will help you better understand what those numbers mean so that you can find the right ones for the job at hand.
Screw dimensions include driver type (flat head, Phillips or hex) length, shank diameter and threads per inch. The last is typically measured in a metric system, with the major diameter being the first number and the thread pitch being the second. This is usually followed by the length in inches, such as: 5/8-24 x 1″, meaning that this particular screw has a major diameter of 5/8″ and 24 threads per inch with a shaft that is 1″ long.
When shopping for screws, it’s important to remember that the head of the screw should not exceed the maximum size of the material into which it will be inserted. Doing so can cause the screw to penetrate too far into the material, resulting in loosening or failure.
It’s also important to keep in mind that the head of the screw should be large enough to be gripped by a tool, such as a wrench or drill. This can be difficult to do with small screws that have very thin heads, so you’ll want to shop for those that are large and have a good shape that will grip well.
Screws come in a variety of materials and styles, including brass, steel, stainless steel, titanium, aluminium, and plastics. Each has its own advantages and disadvantages, so choose the one that is best suited to your project. If possible, purchase screws that have a protective coating to prevent corrosion.
If you need to use the screws for a particularly heavy job, be sure to select the correct gauge. This is determined by the amount of pressure you will be placing on the screw, and a larger gauge is more appropriate for heavier applications.
In terms of head style, flat head screws are great for power drilling and hex head screws are ideal for hex tools. You’ll also want to consider screw length, as longer screws require more force to drive into the material and can cause damage if they’re too short.
Finally, be sure to check your sizing chart for the screw’s thread standards. The most common are coarse (UNC) and fine (UNF), although there is a medium thread standard (M). The chart will also specify the tolerance class, LH or RH symbol, and head style. It should also be noted that there are two diameter systems, inch and metric. Metric sizes are listed in millimeters, beginning with the major diameter and then the thread count. 3/8 in to mm