Screw Sizes – Converting Imperial to Metric

Screws are an excellent way to fasten materials together. But the type and size of screw you use will depend on what your project is, and which materials you are working with. For example, a thin screw may not hold the material you are using, while a thicker screw could damage the surface of the material or cause it to tear. To prevent this from happening, you must use the correct screw for each application.

A screw’s major diameter and pitch are two factors that help you identify its size. The major diameter is the screw’s largest width, while the pitch is the distance between a thread’s point and the next one. Screws are typically measured in either the imperial system or the metric system. The chart below shows the imperial to metric conversions for common screw sizes.

In order to understand screw measurements, it helps to remember the basic premise of how screws are listed on packaging. They usually list the gauge (the screw’s diameter) and the shaft length in inches first, with the thread count and a lettering designation (if applicable) following the second number. For example, a wood screw with a countersunk head will have a “C” followed by the diameter and a number.

For other types of screw heads, such as hex-heads or round headed screws, you will find the head height included in the measurement. This is because the screw head will protrude from the surface of the material it is screwing into. 3/8 lag bolt pilot hole

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