An Introduction and Guide to NPT Gauges

Thread gauges (otherwise known as pitch or screw gauges) are instruments used for reference to estimate the pitch of an object’s thread. Using a gauge requires one to match the thread to the gauge, for which there are various different types, including the NPT thread gauge.

NPT stands for ‘National Pipe Thread’ as this is the standard pipe thread used in America. Its full name is in fact ‘American National Standard Taper Pipe Thread gauges’. There are two types of NPT, one being “male” (external threading), and the other being “female” (internal threading). As with the UNF thread gauge, NPT thread gauges are characterized by its sixty-degree angle and flat tooth shape.

NPT seals are mainly popular in Canada and the US. Its round shape allows the male NPT adapter to screw and wedge it into the female NPT adapter while withstanding enormous amounts of pressure due to the tight and secure fitting. This means sealing the thread is not required as the tapered design is optimal for natural sealing.

NPT is mostly used by petroleum companies, though mainly centered in the States, and are considered "General Purpose" pipe threads because of its versatility and easy assembly.

Two different types of NPT pipe gauges are the NPT L-1 Plug Gauge and the NPT L-1 Ring Gauge.

The NPT L-1 Plug Gauge is a hex gauge design and is used on Internal Taper Pipe Threads. It is used by screwing the plug tight into the thread of the object with the use of your hands until it can go no further and is securely in contact with the end of the thread. You can then gauge if the thread is of acceptable tolerance when the notch on the plug gauge indicates a number not higher or lower than plus/minus one.

The NPT L-1 Ring Gauge, unlike the plug gauge, is characterized by its external application and are used on External Taper Pipe Threads. Once again, the gauge is used by screwing the ring tightly around the external thread of the object with the use of your hands until it can go no further and is securely in contact with the end of the thread. The tolerance of the thread is then gauged by a similar indication of plus or minus one on the gauging face.

It is important for one to make use of thread gauges before making use of the object that has threading as insufficient tolerance may lead to leakage and/or breakage which could quickly become a safety hazard depending on what it is being used for. As NPT is mainly used in petrol companies, leakage of petroleum could definitely lead to disastrous consequences and should be avoided by taking the necessary precautions.

It is easy enough to use thread gauges, as previously indicated, and takes no longer than a minute per thread. It is important the user choose the correct size (which would be specified on the handle) of a gauge that would ensure the threading is of the correct diameter, TPI/pitch and fit.

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