Whether you’re working on plumbing, construction, industrial systems, or irrigation, having a reliable pipe fittings guide is essential — pipes and fittings are the backbone of fluid transport, and choosing the right type ensures safety, durability, and efficiency.

Pipe fittings are used to connect sections of pipe, and the type of fitting you choose depends on its intended function. Since each piping system is unique, the fittings and accessories you require may vary in material, size, and application. Consider your specific needs when selecting the right fitting — are you extending a pipeline, changing its direction, or reducing the flow of water?

The most common pipe fittings and their uses:

*Various Types of Pipe Fittings Used in Plumbing Systems
*Different Varieties of Galvanized Pipe Fittings and Their Uses
*Understanding the Varieties of Grooved Pipe Fittings

There is a wide range of pipe tubing and fitting types, and choosing the right ones is essential for an efficient plumbing system. The most important consideration when selecting tubing and fittings is fixture compatibility. Without this, your plumbing system won’ t operate properly.

Although people often use the terms “pipe” and “tubing” interchangeably, they serve different purposes and are measured differently. Pipes are typically used to transport fluids and gases in large plumbing systems. Tubes, on the other hand, can be square, round, or rectangular and are usually used in structural applications. Selecting the right type of tubing ensures optimal and cost-effective performance.

*Fluid transport: Tubes designed to move fluids from one location to another.
*Structural applications: Tubes used in buildings and frameworks for their mechanical properties.
*Electrical sheathing: Tubes designed to encase electrical wires or components, providing protection against abrasion.

Pipe fittings are typically threaded on both ends, with female threads located on the inside of the fitting and male threads on the outside, which screw into the female threads. One of the most common thread types used in North America is National Pipe Thread (NPT), which features tapered threads designed for both joining and sealing pipes. Fittings are available in male pipe threads (MPT or MNPT) and female pipe threads (FPT or FNPT).

Another widely used thread type is British Standard Pipe (BSP), the standard for plumbing and pipefitting in many countries outside North America. Other thread standards may vary depending on the country and industry.

The choice of fitting material depends on several factors, including temperature conditions, pressure ratings, and cost considerations. Pipes and fittings are both available in a wide range of materials, and fittings are typically matched to the material of the pipe for compatibility and durability.

The most commonly used materials for fittings include both metals and plastics, such as brass, copper, steel, black iron, polyvinyl chloride (PVC), high-density polyethylene (HDPE), and more.

For tubing, the material plays a critical role in selecting the right type for your application. Hard, metal tubing — such as copper, aluminum, and steel — is chosen when strength and rigidity are required, particularly in plumbing and heating systems due to its corrosion-resistant durability.

Soft tubing offers a more flexible alternative, especially in plumbing systems where bendability and easy routing are important. Common plastic materials for soft tubing include nylon, polyethylene, polypropylene, polyurethane, and PVC. Soft tubing not only offers excellent corrosion resistance and strength but also helps reduce the risk of pressure leaks.

Determining the correct pipe size for a project can sometimes be confusing. Pipe size is usually defined by its nominal diameter (DN) or average inside diameter (ID). Pipes with the same nominal size are typically compatible and can be connected easily. The nominal diameter is determined using standardized tables and schedules based on the pipe’s physical dimensions.

Fitting size is based on the inside diameter (ID) of the pipe it connects to and is measured in inches or millimeters. The ID represents the open space inside the pipe, while the outside diameter (OD) refers to the total width of the pipe, including its walls.

Similarly, tubing size is determined by its OD, ID, and wall thickness, and is also measured in inches or millimeters. Unlike pipes, tubing nominal sizes are typically based on the outside diameter.

Careful measurement is essential to ensure correct sizing. Choosing the appropriate tubing and pipe fitting types will help your plumbing system operate efficiently and reliably.

Q: What does Nominal Pipe Size (NPS) mean?

A:Nominal Pipe Size (NPS) is a standardized North American system used to describe the approximate size of pipes. Although the term suggests a specific measurement, NPS actually refers to the nominal (named) dimension rather than the precise internal or external diameter of the pipe. It was originally based on the internal diameter (ID) of steel pipes but, as wall thicknesses evolved, NPS became more of a reference label rather than an exact measurement. NPS is usually expressed in inches (e.g., NPS 2) and helps engineers, plumbers, and contractors select compatible fittings and components for piping systems.

Q: Is the Nominal Diameter (ND) the same as the Nominal Pipe Size (NPS)?

A:No, they are not the same, although they are often confused.
Nominal Diameter (ND) — also called Diameter Nominal (DN) — is part of the metric measurement system and refers to the approximate outside diameter (OD) of pipes, rounded to the nearest convenient number in millimeters.
On the other hand, Nominal Pipe Size (NPS) is the imperial system equivalent, measured in inches, primarily used in the U.S. and Canada. Both terms simplify pipe classification but refer to different measuring systems: ND (DN) is metric, NPS is imperial.

Q: How is pipe size measured?

A:Pipe size can be determined in several ways, depending on the type of pipe and system. Generally, the two most important measurements are:

*Outside Diameter (OD) — the measurement across the outer edge of the pipe.
*Nominal Pipe Size (NPS) — the standardized size label.

In many cases, especially for PVC and metal pipes, the size information is printed directly on the pipe’s surface, including the NPS, material type, and wall thickness (schedule). If markings are unavailable or hard to read, the size can be measured manually.

For accessible pipe ends, use a ruler, tape measure, or caliper to measure either the OD or ID. If the pipe is installed and only the exterior is visible, measure the OD directly. If the pipe end is open and accessible, you can measure the ID to identify the size. Once measured, compare the result to a pipe size chart to match it to the correct NPS or DN classification.

Q: How do I measure the diameter of a pipe?

A:Before measuring, it’s important to know whether the pipe has male threads, female threads, or no threads at all, as the measuring method will vary.
*Male threads are found on the exterior and are easily visible as spiral ridges around the pipe.
*Female threads are located inside the fitting and can be harder to spot from the outside.

Here’s how to measure each type:

For Male Threads:
1.Use a flexible tape measure or wrap a string around the outside of the pipe to measure the Outside Diameter (OD).
2.If using string, mark the point where the string overlaps, then measure the total length between the tip and the mark.
3.Divide this measurement (the circumference) by 3.1416 (π) to calculate the OD.
4.Cross-reference the OD using a nominal pipe size chart to determine the correct NPS.

For Female Threads:
1.Use a ruler or caliper to measure the Inside Diameter (ID) of the pipe or fitting.
2.Measure across the hollow opening, from one inner edge directly to the opposite inner edge.
3.Refer to a pipe size chart to match your measurement with the correct NPS or DN.

Always use precise measuring tools, like calipers, especially for metal or small-diameter pipes, to avoid incorrect fitting selection. Pipe size accuracy is crucial for both leak prevention and maintaining system performance.