Tube fittings connect tubing, hoses, and fluid power components so hydraulic, pneumatic, and instrumentation systems can route flow safely and reliably. For someone new to fluid power, fitting terminology can be confusing because a single fitting may include tube size, dash size, port style, thread type, shape, and end configuration.
This Tube Fittings 101 guide explains the basics, including what tube fittings do, how tube OD affects fitting size, what dash size means, the difference between a port end and a tube or hose end, and common fitting configurations such as straights, elbows, tees, and crosses.
Understanding these basics can make it easier to identify the right fitting, communicate with a supplier, and avoid mismatched components in hydraulic, pneumatic, and lubrication systems.
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Tube fittings are connectors used to join tubing to other tubing, hose, or fluid power components such as pumps, valves, cylinders, manifolds, and instrumentation. Their main job is to create a secure connection that can hold pressure, seal properly, and allow fluid or air to move through the system without leaks.
In fluid power systems, tube fittings are commonly used in hydraulic, pneumatic, lubrication, and instrumentation applications. The right fitting depends on the tube outside diameter, connection type, port style, thread type, pressure requirements, material, and the direction the tube or hose needs to run.
Tube fittings can connect:
These fittings have two major functions: sealing under pressure and holding the tube under pressure. The goal is to create a reliable transition from one piece of the system to another.
| Term | What It Means | Why It Matters |
|---|---|---|
| Tube OD | The outside diameter of the tube. | Fitting size is based on tube OD, not the outside dimensions of the fitting. |
| Dash size | A size designation based on sixteenths of an inch. | A 1/2-inch tube OD corresponds to a -8 fitting size. |
| Tube end | The end of the fitting that connects to tubing or hose. | It must match the tube or hose size and connection style. |
| Port end | The end of the fitting that connects into a component such as a pump, valve, cylinder, or manifold. | It must match the component port and thread type. |
| Configuration | The shape and layout of the fitting, such as straight, elbow, tee, or cross. | It determines how tubing is routed through the system. |
When selecting tube fittings, size is based on the tube OD, or outside diameter. The size designation does not refer to the outside dimensions of the fitting itself. Instead, it refers to the tube outside diameter the fitting is designed to work with.
This is one of the most important basics to understand. If the tube OD is wrong, the fitting will not properly match the tube, which can create sealing, assembly, or performance issues.
Figure 1: Tube and tube OD
Once you know the tube OD, you can understand fitting dash size. Dash size is a common way to describe fitting size based on sixteenths of an inch. To calculate dash size, multiply the tube OD by 16.
For example, a 1/2-inch OD tube multiplied by 16 equals 8. That means a 1/2-inch OD tube would use a -8 fitting. You can also reverse the calculation: 8 divided by 16 equals 1/2, so a -8 fitting corresponds to a 1/2-inch OD tube.
Note: Metric fittings use different nomenclature and do not follow the same dash-size rules.
Figure 2: Size 8 fitting
A tube fitting is a connector between parts of a fluid power system. There are two common connection points, or ends, that may be called out on a tube fitting: the tube end and the port end.
The tube end connects to tubing or hose. The port end connects into a component such as a pump, valve, cylinder, manifold, or other system component. The port end allows the fitting to act as a bridge between the tube or hose and the component.
A fitting with both a port end and a tube or hose end is commonly referred to as an adapter. For example, an adapter may be used to connect a tube directly to a pump. Many end configurations are possible, including tube-to-tube, tube-to-port, tube-to-hose, and multi-end configurations.
Figure 3: Port and tube end fitting
Tube fittings are available in many configurations. At a basic level, these configurations can be grouped into straights and shapes.
Straight fittings connect components in a direct line. Shaped fittings are used when tubing needs to change direction, split flow, or connect multiple lines. Common fitting shapes include 90-degree elbows, 45-degree elbows, tees, and crosses.
The ends of each fitting can also vary. A fitting may have all tube ends, one tube end with one port end, two tube ends with one port end, or other combinations depending on the application.
Figure 4: Assortment of fitting configurations
Choosing the right tube fitting starts with the tube outside diameter, system pressure, fluid or air media, material requirements, port style, thread type, and routing needs. The fitting must match the tube or hose end, connect properly to the component port, and support the pressure and environmental conditions of the application.
It is also important to consider the fitting configuration. Straight fittings are used when the connection can run directly from one point to another, while elbows, tees, and crosses help route tubing around equipment, split flow paths, or connect multiple lines within the system.
If you are unsure which fitting size, end style, or configuration is right for your application, MCE can help identify the correct tube fitting or hose adapter based on your system requirements.
Need help identifying the right tube fitting? MCE can help match tube OD, dash size, port style, material, and configuration to your hydraulic, pneumatic, lubrication, or instrumentation system.
Get local support at one of our Parkerstores >>
Source: Parker: First Day with Tube Fittings: Fittings 101 the Basics