How do you choose pneumatic fittings and tubing correctly?
Pneumatic fittings connect tubing quickly and tightly to valves, cylinders and air units. The right choice depends on tube outer diameter, thread type, material and shape. This guide explains the selection criteria and shows common sizes in a clear overview.
Go to Pneumatics & HydraulicsWhat do push-in fittings do and how are they built?
Push-in fittings connect pneumatic tubing without tools: the tube is inserted, a collet grips it, and a seal secures the connection. To release, you press the release ring. They are the standard for fast, repeatable assembly on valves, cylinders and air preparation units.
A fitting has two sides: the tube side, defined by the tube outer diameter, and the device side with a thread. Both sides must match the components they join. In addition, material and shape determine how flexible, chemically resistant and space-saving the line can be routed.
How do you choose diameter, thread and material?
First match the tube outer diameter to the fitting (commonly 4, 6, 8, 10, 12 mm) and choose the device thread to suit the component. Cylindrical G (BSPP) threads seal via an O-ring or gasket, tapered R (BSPT) threads seal in the thread itself, usually with a sealant.
| Tube outer Ø | Typical inner Ø | Common thread | Typical use |
|---|---|---|---|
| 4 mm | approx. 2.5 mm | M5, G1/8 | Small cylinders, sensors, signal air |
| 6 mm | approx. 4 mm | G1/8, R1/8 | Standard actuation, short runs |
| 8 mm | approx. 5-6 mm | G1/4, R1/4 | Medium cylinders, main distribution |
| 10 mm | approx. 6.5-8 mm | G1/4, G3/8 | Higher flow rate |
| 12 mm | approx. 8-9 mm | G3/8, G1/2 | Large cylinders, main lines |
How do you seal and assemble fittings correctly?
Tapered R (BSPT) threads are assembled with a sealant such as PTFE tape or thread locker and seal in the thread. Cylindrical G (BSPP) threads seal on the face via an O-ring or gasket. Many fittings already come with the seal pre-fitted.
Frequently asked questions
What is the difference between G and R threads?
G (BSPP) is a cylindrical thread that seals via an O-ring or gasket on the face. R (BSPT) is tapered and seals in the thread itself, usually with PTFE tape or thread locker. Make sure the fitting and the component match each other.
How do I find the right tube diameter?
A fitting is made for a fixed tube outer diameter, commonly 4, 6, 8, 10 or 12 mm. The outer diameter must match exactly. For air volume the inner diameter also matters - choose larger for long runs or big cylinders.
Which tube material is right?
PU is very flexible and suits moving applications with a tight bend radius. PA (nylon) is more rigid and pressure-resistant for fixed routing. PTFE is used for chemicals and high temperatures. Check the medium, temperature and routing type.
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Right sizes
Overview of common diameters and threads.
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