To determine if a thread is NPT (National Pipe Taper), there are a few methods you can use. One of the most common and accurate methods is to measure the diameter of the 2nd or 3rd thread using a caliper. This will give you an accurate measurement that can be cross-referenced with a chart to determine the NPT size.
Here are the steps to follow:
1. Start by selecting a caliper that is suitable for the size of the thread you are measuring. Calipers come in various sizes, so make sure you have one that can accurately measure the diameter of the thread.
2. Carefully position the caliper around the thread, ensuring that it is aligned properly and not tilted at an angle. The jaws of the caliper should be perpendicular to the thread to get an accurate measurement.
3. Gently close the caliper until the jaws make contact with the thread. Be careful not to apply too much pressure, as this may distort the measurement.
4. Take note of the measurement displayed on the caliper. It is important to measure the diameter of the thread, not the overall size of the pipe, fitting, or valve.
5. Once you have the measurement, refer to a chart that provides the nominal NPT pipe sizes based on the caliper measurement. These charts can be easily found online or in plumbing reference books.
6. Cross-reference your caliper measurement with the chart to determine the NPT size. The chart will provide you with the corresponding NPT size based on the measured diameter of the thread.
It’s important to note that the actual measurement you obtain from the caliper will not be the same as the NPT pipe size. The NPT pipe size refers to the nominal size of the pipe, fitting, or valve, while the measurement you obtain is the actual diameter of the thread.
In some cases, you may find that the measured diameter falls between two NPT sizes on the chart. In such instances, it is generally recommended to choose the larger NPT size to ensure a proper fit.
If you are unsure or still have difficulty determining the NPT size, it may be helpful to consult a professional or refer to a plumbing specialist who can assist you in accurately identifying the thread type.
By using a caliper to measure the diameter of the 2nd or 3rd thread and cross-referencing the measurement with a chart, you can determine the NPT size of a pipe, fitting, or valve. It is important to be accurate in your measurements and to consult reliable references to ensure the correct identification of the thread type.