Pneumatic tubing 6/4 and 8/6: the short answer
In German pneumatics a tube is named by outside and inside diameter: 6/4 means 6 mm OD and 4 mm ID, so a wall of 1.0 mm; 8/6 means 8 mm OD and 6 mm ID, also a wall of 1.0 mm. The OD is the size that has to match the fitting. At the same OD, the thicker wall of an 8/5 tube (1.5 mm) carries more pressure than an 8/6 tube.
How 6/4 and 8/6 are written
Our model numbers write the same sizes as four digits: 0640 is 6 mm OD and 4 mm ID, 0860 is 8 mm OD and 6 mm ID. The wall thickness is (OD minus ID) divided by 2. Use the unit converter to calculate it for any size.
Working pressure and bend radius at 6/4, 8/6 and 8/5
The table lists the working pressure in bar at 23 °C and the minimum bend radius in mm from our model tables. The PU tubing table is shown with its bend radius only; read the working pressure of PU tubing on the PU tubing page.
| Size (OD/ID) | Material | Model | Working pressure (bar) | Min. bend radius (mm) |
|---|---|---|---|---|
| 6/4 | PU | YN-PU 0640 | see product page | 15 |
| 6/4 | Polyether | YN-PUR 0640 | 10 | 25 |
| 6/4 | PA6 | YN-PA6 0640 | 35 | 35 |
| 6/4 | PA12 | YN-PA12 0640 | 27 | 30 |
| 6/4 | Composite V8 (PU outer layer) | YN-0640 V8 | 14 | 15 |
| 6/4 | Composite V9 (polyether TPU outer layer) | YN-0640 V9 | 14 | 16 |
| 8/6 | PU | YN-PU 0860 | see product page | 25 |
| 8/6 | Polyether | YN-PUR 0860 | 8 | 40 |
| 8/6 | PA6 | YN-PA6 0860 | 23 | 48 |
| 8/6 | PA12 | YN-PA12 0860 | 17 | 50 |
| 8/6 | Composite V8 (PU outer layer) | YN-0860 V8 | 12 | 20 |
| 8/6 | Composite V9 (polyether TPU outer layer) | YN-0860 V9 | 12 | 29 |
| 8/5 | PU | YN-PU 0850 | see product page | 20 |
| 8/5 | Polyether | YN-PUR 0850 | 12 | 30 |
| 8/5 | PA6 | YN-PA6 0850 | 28 | 45 |
| 8/5 | PA12 | YN-PA12 0850 | 29 | 30 |
| 8/5 | Composite V8 (PU outer layer) | YN-0850 V8 | 15 | 20 |
| 8/5 | Composite V9 (polyether TPU outer layer) | YN-0850 V9 | 15 | 29 |
Three patterns stand out. PA6 carries the highest working pressure at 6/4 and 8/6. At 8/5, PA12 matches PA6, and every material carries more than at 8/6, because the wall is 1.5 mm instead of 1.0 mm. And PU, polyether and composite tubes bend at a smaller radius than PA6 at the same size.
Which material for 6/4 or 8/6
- PU and polyether: flexible, tight bend radius, for moving connections and short runs. See polyether tubing.
- PA6: the highest working pressure of the four, firmer, larger bend radius. See PA6 nylon tubing.
- PA12: usually more flexible than PA6 (a smaller bend radius at 6/4 and 8/5, about the same at 8/6), for routing where pressure also matters. See PA12 tubing and the PA6 vs PA12 comparison.
- Composite: a PU or polyether TPU outer layer over a PA12 inner layer. See composite tubing.
For PU or nylon, the PU vs nylon selection checklist walks through flexibility, pressure, temperature and fitting hold.
Matching the fitting
- A 6 mm push-in fitting takes a 6 mm OD tube; an 8 mm fitting takes an 8 mm tube. The ID does not set the fitting size.
- A 6 mm tube is not a 1/4 in tube. The two differ by 0.35 mm, more than the tolerance of ±0.10 mm on our nylon tubing. Do not mix metric tubes with inch fittings.
- The wall matters too: at 8 mm OD, 8/5, 8/5.5 and 8/6 tubes have the same OD but different pressure ratings. See matching tubing to fittings.
Frequently asked questions
What does 6/4 mean on a pneumatic tube?
It is the outside and the inside diameter in mm: 6 mm OD and 4 mm ID, which gives a wall of 1.0 mm.
Is 8/6 or 8/5 better for higher pressure?
8/5. At the same 8 mm OD, the 1.5 mm wall of an 8/5 tube carries more pressure than the 1.0 mm wall of an 8/6 tube. For PA12 the working pressures in our tables are 29 bar at 8/5 and 17 bar at 8/6.
Which tube fits a 6 mm push-in fitting?
A tube with a 6 mm outside diameter, for example 6/4. Check the fitting maker’s data for the wall range it accepts.
Can I use PU tubing at 6/4 in place of nylon?
Only if the working pressure and temperature of your circuit are within the PU rating. Nylon carries more pressure at 6/4, while PU bends at a smaller radius. Compare both on the data sheets.
Request a sample
request a 1 to 3 m sample at your size, or see the full size chart for sizes beyond 6/4 and 8/6: send your requirements.
Sources and scope
- PU Tubing — English data sheet (v3-20261020)
- PA6 Nylon Tubing — English data sheet (v4-20261020)
- PA12 Nylon Tubing — English data sheet (v5-20261020)
Use these documents for the identified product models and stated test conditions. General material comparisons and selection checklists do not establish a different grade’s rating, fitting compatibility or project approval. Confirm the exact model, medium, temperature, pressure and required evidence before ordering.
Content review: zhangkexin · Marketing
Review scope: market information and document references.
