G-series is the most important method of measurement for pipe threads, which is known as British pipe thread. it is important to know how you can convert the G-series to metric standard or millimeter to be able to measure the pipe and thread dimensions via a caliper and have a good sense of the dimensions. Although the metric standard has replaced British standards in many cases, the pipe thread standard is still used in inch in many pneumatic, plumbing, hydraulic, etc., connections and it’s useful to know how you can convert between these standards.
In the following table, you can find the equivalent dimension for any G-series size. Here is a short guide for how to convert the G-series thread standard to the metric system.
For example, the “1/8” thread size in the first row is used for various pneumatic connections, and the conversion is as follows: For this thread size, the outer diameter of the threads is approximately 9.7 millimeters, the thread pitch is approximately 0.9 millimeters, the number of threads per inch is 28, and the required hole diameter for tapping this thread is 8.7 millimeters.
