Choosing the right screw for the job is a crucial part of construction work, from woodworking to metal roofing. Choose the wrong size and your screws may split the wood, cause thread damage or even compromise structural integrity. Unlike nails, which are measured by the length of their shafts, screws are sized in terms of their gauge, threads per inch and head diameter. Our guide to 1/4 screw diameter explains these measurements and how they apply to various types of screws.
The first number on a screw callout is the gauge size, also called the major diameter of the screw thread. Screws with a major diameter less than 1/4 inch are labeled in sizes #0 through #12, with each successive number increasing by.013. In addition, each screw gauge has a decimal equivalent; for example, the decimal equivalent of a #8 screw is.164. Screws with a major diameter of more than 1/4 inch are often labeled by their type and class, for example Duraspin. The last number on a screw callout is the threads per inch (TPI), which specifies how many threads are in one inch of a screw. For example, a screw with a thread count of 32 is considered coarse, while 36 TPI is fine. A screw’s threads are measured using a thread gauge, which consists of numerous strips of metal with different number of threads cut into them. You can measure the pitch of a screw’s threads by systematically working your way through the different strips until you find one that matches the screw’s pitch.
Screws are also rated for their strength and corrosion resistance. For example, a Grade-8 screw is heat-treated and oil-quenched to meet higher tensile strengths than a regular Grade-5 screw, while a stainless steel screws has corrosion-resistant properties.
Whether you’re trying to figure out how big your screw heads are or just trying to understand the information on a screw box, knowing about screw sizing will make it much easier to find the perfect parts for your next project. To help you get started, this guide explains the three main screw measurements: gauge, threads per inch and shaft length.
In addition to a screw’s gauge, threads and head diameter, the callout on a screw box may also specify its tolerance class, the LH symbol if it is left-handed, and its shaft length. It may also specify the head style and a thread standard, for example coarse (UNC) or fine (UNEF). Lastly, it will usually list its threads-per-inch (TPI). To learn more about these screw specifications, check out our article on Screw Thread Sizing: What Are the Standard Screw Threads for Your Tools. 1/4 screw diameter