Screw Size Chart – How to Read a Screw Label
Choosing the correct size screw for your project can make or break the overall outcome of the finished work. Whether you’re putting together furniture or installing a metal roof, if you use the wrong screw it can cause damage or weaken the material. Screws are labeled with three essential measurements – gauge, length and threads per inch (TPI). There are a number of different types and sizes of screws, and knowing how to read their labels can help you determine which type is right for your job.
The first number on a screw’s label is the gauge, which refers to the diameter of the shaft – the part that goes into the material. The second number is the length of the screw – this is the distance from the flat bottom of the head to the tip or blunt end. The last number on the screw’s label is the threads per inch – this is the number of threads that are in one inch of the screw’s length. For example, a screw labeled 10 x 2 has a diameter of 2 inches and 36 threads per inch.
Screws sold with imperial system measurements often have the gauge and length listed first, and don’t usually include a thread count. They may also have a letter after the length to indicate if it’s coarse or fine, and a symbol to indicate if it’s left-handed (LH). Screws that are metric in origin typically list the diameter of the screw thread in mm first, followed by the length of the screw, and then the threads per inch. screw size chart
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