The Basics of Tube Fittings

What is Tube Fitting?

Tubes are a type of pipe used to move water, gas, oil, or other materials. They can either be metal or plastic. They come in various shapes and sizes and can be bought already fitted, or you can buy them Open-ended. Tube fitting connects runs of tubes to other tubing sections or pipes.

Types of Fittings

1. Concentric Tube Fitting

A concentric instrumentation tube fitting is an outer tube concentric with the inner tube. This means that the inner and outer tubes are not connected but connected by a flange. These fittings have been used for many years and can easily be recognized by their distinct shape.

2. Solenoid Tube Fitting

A solenoid fitting is an outer tube that is not concentric with the inner tube but instead connects to the inner tube, similar to how a solenoid works. A solenoid works by using electromagnetic fields to create an electric current that causes material on one end of the tube to move in response to the current flowing through it.

3. Compression Fitting

A compression fitting is a fitting with two tubes connected using a compression ring. This is a very common type of fitting and can be found on many different types of tubing.

4. Coupling Tube Fitting

A coupling tube fitting is a fitting with two tubes connected using a coupling ring or flange. These fittings are commonly used in the medical field because they allow the tubes to be disconnected when they don’t need to be.

5. Joint Fitting

A joint fitting is a fitting with two tubes connected using a long tube that connects to another. These fittings are typically used for connecting oil lines together. They have become more popular over the years because they provide an easy way to connect oil lines without having to worry about leaks or damage from over-tightening or under-tightening connections.

Application of Tube Fitting

1. Hydraulics Applications

Tubing is used in the hydraulics industry for many different things. One of the most common uses for tubing is to connect hydraulic hoses. It can also be used to help increase the strength of hydraulic hoses, and it can also help prevent fluid from leaking and are often resistant to rusting.

2. Piping Applications

Tubing is often used as piping in various industries, such as plumbing and electrical. Tubing is used to connect pipes, and it can be found on all types of piping systems, including plumbing, irrigation, heating, cooling systems, and much more.

3. Pneumatic Applications

They transfer gasses from one place to another; they have tight seals to prevent gas leakage and are resistant to corrosion. The most standard pneumatic tubing applications include air hoses, airlines, and gas lines.

Function of Tube Fittings

There are different types of fitting installed in tubing systems, and they perform other functions.

1. Fittings That Extend or Terminate Tube Length

They connect to other tubes of similar type or different ones through welding, soldering, or threading. They are also used as a seal to mark the end of the tube; they include an adapter, coupling, sleeve, cap, and plug.

2. Fittings That Add or Change the Direction of Flow

They are used to connect two tubes of different diameters or different types. Examples include; elbow, tee, wye, and cross.

3. Fittings that Maintain Pressure, Temperature, and Chemical Composition

They are used to control the fluid’s pressure, temperature, or chemical composition flowing through them. They are also installed in heating and cooling systems which need to maintain constant pressure and temperature against the environment.

4. Fittings that Restrict the Flow

They help maintain a specified flow rate by limiting the amount of fluid passing through them. They include check valves, ball valves, butterfly valves, etc.

Categories of Tube Fittings and Adapters

1. Accessories

Pipe fittings that connect or smooth some tubing to another. An adapter connects to well-designed extensions of pipes and fittings.

2. Manufacturing Techniques

Tubing connectors use three different production techniques. These include threading, turning, and welding. Welding is the hot gas welding process that creates a permanently stable connection at a high temperature.


1. Sizing and Tolerances

Size of the fitting is usually given in millimeters or inches, following the international standard BS EN ISO 527.2

The wall thickness of the tubing is specified by the material it is made from. The most common are; steel, brass, copper, and plastics. If a tube has a diameter less than the wall thickness, it will have to be reinforced to prevent buckling or cracking. If a tube has a wall thickness greater than its diameter, it will have to be reduced in size or strengthened to avoid buckling or cracking. The manufacturer specifies tolerances for each tube type by their standard methods.

2. Materials

All materials used in fitting are specified by their properties and requirements for a particular application. Materials are either metals or plastics. Examples of metals include brass, Aluminum, stainless steel, and copper. Examples of plastics include polyethylene, high-density polyethylene (HDPE), polyvinyl chloride (PVC), acrylics, and so on.

3. Environments of Use

Environmental conditions which affect a fitting include; temperature (temperature range or design), pressure (design pressure or working pressure), chemical composition (design chemical composition or working chemical composition), and humidity (design humidity or working humidity).

Tube fittings and adapter fittings are used extensively in many chemical industries, especially heavy chemical plants. Plastic tubing is also used extensively in domestic plumbing applications and irrigation. Fluid-through fittings form an integral part of the piping (sometimes called piping systems) systems in industrial and domestic plumbing applications.

A flexible metal pipe with a similar shape to an upside-down funnel or hose- most commonly is used for wastewater management. It has threads inside to facilitate screw connections for pollution dispensers, plumbing waste valves, and potable water. The vertical surface of the inside of this fitting is smooth and often black.


To find the correct specification to suit a given tube fitting design, a work down table showing a product listing of different trade level standards relevant to plastic tubing in use. High quality and easy-to-use tube fitting help plumbers and other engineers obtain a quality tube, and pressure fitting enables them to use the tubes efficiently.

Jeff Campbell