How To Determine Pipe Thread Size for End Caps

How To Determine Pipe Thread Size for End Caps

Pipes are an integral part of the structures we see every day, and experts use a considerable amount of applied science for their construction. Pipe threading is an important part of the pipe manufacturing process, and it determines other aspects of the pip, such as which end cap will fit correctly. Read on to learn how the pipe thread’s measurements connect to the correct end cap.

The Importance of Threaded Pipes

Many of us are familiar with pipes that feature rows of horizontal lines on their ends and look similar to a screw. These parts have pipe threads that screw into receiving pieces with a similar pattern. Other pipes, end caps, couplers, and other fittings will connect to a threaded pipe to create a piping system for the infrastructure of buildings.

Pipe threads improve security within a system of pipes and create a tighter seal when the pipe screws into an attached piece. This increased security makes transporting fluids such as water or oil easy and prevents leakage as the liquid transfers through a connected pipe.

What Is Pipe Thread Size?

The pipe thread is measured in centimeters. This measurement gives information for understanding the pipe size and finding the correct fittings. The width between threads coordinate with threads of a similar spacing on the receiving end of another pipe or fitting.

National Pipe Thread (NPT) Standards

All manufactured pipes made in the US follow a size that adheres to the National Pipe Thread (NPT) standard. Pipe manufacturers follow NPT standards for easier manufacturing of pipes and the pieces that connect them. The measurements overviewed in NPT standards account for various factors, such as the pipe’s interior or exterior diameter and the size of the threads, to create an approximate value.

How To Determine Pipe Thread Size

There are different ways someone may determine the thread size of a pipe. Precision is important when taking these measurements, as it will help you avoid wasting time searching for the correct fitting or attachment.

Taking Measurements

A quick way to determine a pipe’s thread size is by taking measurements. Wrap a tape measure around the pipe to find the diameter of a thread. You’ll need to measure the exterior diameter for male ends and the interior for female ends.

If you use a tape measure, mark the measurement from where you start to where the end connects for greater precision. If your calculations are even a centimeter off, you may associate the pipe with the wrong NPT standard value and use incorrect fittings.

The width of the threads will help you determine the size of the pipe. The threads will shrink as the pipe’s diameter increases, so it’s possible to determine a pipe’s thread size based on whether the pipe is larger or smaller. Measuring one thread will provide you with enough information to determine how large the rest of the threads are and what the pipe’s size is.

Using the NPT Standard Chart

The National Pipe Thread standard also provides a chart that people can use to help them find the correct size of a pipe and its threads. This chart shows how most pipe manufacturers make their pipes and will help you find the correct size for the pipe you’re measuring.

The chart provides a variety of information, giving values for how many threads a pipe has and values for interior and exterior pipe diameters. Despite the variations, the national standard for approximation will show on the chart and may begin at 1/8 inch and reach as high as 5 inches in diameter.


Aside from a tape measure, certain tools will help you measure the pipe thread size. For instance, a template will provide hole sizes that determine the exact diameter of the pipe and make measurements easier.

A pitch thread is also a useful tool for simple measurements. The pitch thread will match one of the gauges to the threads along the pipe. The “leaf” of the tool presses into the threads and determines if the teeth of the leaf are pressing against the threads or between them. If the teeth match the spacing of the threads, that leaf is the correct measurement. The leaf will have a centimeter mount etched into its surface that tells you the measurements.

The Purpose of End Caps for Pipes

As pipes transfer a substance from one point to another, they may need an attachment to seal an open end. These attachments may include an end cap that screws onto the pipe threading to prevent leakage and keep contaminants out. End caps are essential for every pipe to seal off ends that aren’t necessary for transferring substances in a pipe system.

The Connection Between Thread Size and End Caps

The thread size of a pipe and the size of the end cap share a connection in manufacturing. It’s important to determine the thread size of a pipe for the end cap to ensure it fits properly, as a loose or ill-fitting cap will eventually lead to leakage. The above methods will help you find the measurements you need to ensure you use the correct end cap and prevent malfunction.

Which Measurements To Use

The way you measure the pipe threads may lead to different results that could affect your decision of which end cap to use. All attachments you use should adhere to the nominal pipe measurement shown on an NPT standard chart, not the measurements you’ve taken. All pipe threads are manufactured to feature exact measurements that adhere to NPT standards, which is why you must always refer to this chart.

The measurements you make are only for determining the pipe thread size for end caps. But the end cap will screw onto the pipes based on nominal measurements instead of personal estimates.

For example, if you have a threaded pipe with a 2-inch thread diameter and a thread size of 1 3/4 inches, you wouldn’t find an end cap with a 1 3/4-inch diameter. Instead, you would find a 2-inch diameter cap to fit the 2-inch pipe.

Does the Type of End Cap Matter?

End caps consist of various materials with different benefits. Plastic end caps for pipes have the benefit of corrosion resistance and will last for years, depending on the conditions surrounding the pipe. Metal end caps are great for creating a solid endpoint that will enhance the security of the pipe and make a metal-to-metal seal.

You have numerous options for how you wish to seal your pipe, but it is important to have an end cap regardless of pipe type. The assurance that the contents inside the pipe won’t leak is an essential element of a reliable pipe system.

A pipe’s thread size is important in finding the right end cap. The best end cap will fit onto the pipe threading and tightly seal it, improving the pipe’s structure while preventing leakage and contamination.

How To Determine Pipe Thread Size for End Caps

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