How to Choose the Right Fittings

There is a wide selection of pipe tubing and pipe fitting types and finding the right ones for your pipes is essential to 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.

Here’s what to consider when choosing pipe tubing and fittings:

Pipe vs. Tubing 

Although people might use the terms “pipe” and “tubing” interchangeably, they have different purposes and are not measured the same way. Pipes serve as a vessel to transfer fluids and gases in large plumbing applications. Tubes, on the other hand, can be square, round or rectangular and are typically used in structural applications. Selecting the right type of tubing helps ensure optimal and cost-effective plumbing performance. 

Tubing can be made from hard or soft materials. However, tubing usage falls into three main categories:  

• Fluid transport: tubes that transport fluids from one place to another
• Structural applications: tubes designed to use in buildings and structures with mechanical properties
• Electrical sheathing: tubes that are designed around electrical wires or applications to protect against abrasion   

Thread Types

Pipe fittings are threaded on both ends, with female threads on the inside of a fitting. Male threads are on the outside of a fitting and screw into the female threads. A common thread type used in North America is National Pipe Thread (NPT), featuring tapered threads used for joining and sealing pipes. Fittings come in male pipe threading (MPT or MNPT) and female pipe threading (FPT or FNPT). Another common thread type is British Standard Pipe (BSP), the standard used in most countries for plumbing and pipefitting. Other thread-type standards vary based on the country and industry.

Material

The material of fittings depends on several factors, including temperature conditions, pressure ratings and cost. Pipes come in a wide variety of materials, as do fittings. However, both fittings and tubing components are typically matched with the material of the pipe itself. The most common materials for fittings are metals and plastics, including brass, copper, steel, black iron, polyvinyl chloride (PVC), high-density polyethylene and more.

For tubing, the material plays a huge role in determining the right kind for your application. Hard, metal pipe tubing is used when pipes need strength and hardness. Copper, aluminum and steel are the most commonly used metals for tubing. These materials are frequently used in plumbing and heating applications for their corrosion-resistant durability. Soft tubing is a more flexible alternative in plumbing systems. The most commonly used plastics are nylon, polyethylene, polypropylene, polyurethane and PVC. Soft tubing offers corrosion resistance, strength and helps reduce pressure leaks.

Size

Finding what size pipes are needed for a project can be confusing. However, pipe size refers to the nominal diameter (DN) or average inside diameter of the pipe measurement. Pipes can be easily interchanged and connected to the same nominal diameter pipes. The nominal diameter can be calculated using standard tables and schedules based on the pipe dimensions. 

Fitting size is determined by the inside diameter (ID) of the pipe it’s connecting to and is measured in inches or millimeters. ID measures the size of the empty portion of the cylinder, and OD sizes the thickness of the tubing wall.

The tubing size is somewhat similar. The dimensions for tube sizing are determined by the OD, ID and wall thickness and measured in inches or millimeters. Nominal sizes for tubes are based on the outside diameter.

Taking time to measure carefully will help ensure your sizing is correct. Selecting the proper tubing and pipe fitting types ensures your plumbing system can operate at peak performance.

Pipe & Pipe Fitting Basics

With any major plumbing jobs, you will likely need pipe and pipe fittings. Pipe fittings are plumbing parts used to connect different sections of a pipe. Pipe fittings are available in various shapes and sizes, and are essential when trying to fit pipes where needed, around corners, underground, or up a wall.

Purpose & Types of Pipe Fittings

The shapes, sizes, and material of pipe fittings vary with the purpose. Typically the pipe fitting material should be the same as the pipe being fitted.

The chart below shows common uses and pipe fitting types:

Pipe Fitting Purpose

Pipe Fitting

Couplings, Adapters, Unions, Caps, and Plugs Pipe

Purpose

Extend or seal a pipe

Pipe Fitting

Elbows

Purpose

Change a pipe's direction

Pipe Fitting

Tees, Cross, Side-inlet Elbows, Wyes

Purpose

Connect two or more pipes

Pipe Fitting

Reducers, Bushings, Couplings

Purpose

Change pipe size

Pipe Fitting

Valves

Purpose

Change direction of the flow

Pipe Fitting Connections

The type of pipe material, shape, and size, will determine the type of connection you need for your pipe fittings.

• Threaded pipes attach by screwing together. The pipe will have either exterior (male) threads or interior (female) threads to connect
• Slip fit, crimp, and clamp connections use sleeves, rings, or clamps that fit over the pipes once they are connected
• Push-to-Connect fittings such as SharkBite ® , connect easily when pushed into place
• Sweat fittings require the use of solder at the connection
• Solvent weld fittings connect with quick-drying solvent cement
• Compression connect threaded pipes with a nut and ferrule

Selecting Pipe Fittings

When trying to find the right pipe fittings for the job, there are few key things to keep in mind:

• Material—The fitting must be compatible with the pipes and the fluids it will carry
• Temperature and Pressure—Be sure the temperature and pressure ratings are appropriate for the situation
• Design and Application—Choose right size and type of fitting for job

The reliability of any pipe fitting depends on proper installation and application.