Tube sizes & wall thickness
Specify stainless steel tubing by its outside diameter and wall thickness. Use these reference dimensions to start an enquiry, then confirm grade, length and service requirements.
Find a reference size
Selected dimensions below appear in the supplied Fluidline tubing tables. This is a quotation aid, not a live stock list or a pressure approval. Other dimensions can be discussed with Fluidline.
| System | Tube outside diameter | Wall thickness | Request a quote |
|---|---|---|---|
| Metric | 6 mm | 1.0 mm | Enquire → |
| Metric | 6 mm | 1.2 mm | Enquire → |
| Metric | 6 mm | 1.5 mm | Enquire → |
| Metric | 8 mm | 1.0 mm | Enquire → |
| Metric | 8 mm | 1.2 mm | Enquire → |
| Metric | 10 mm | 1.0 mm | Enquire → |
| Metric | 10 mm | 1.5 mm | Enquire → |
| Metric | 12 mm | 1.0 mm | Enquire → |
| Metric | 12 mm | 1.5 mm | Enquire → |
| Metric | 12 mm | 2.0 mm | Enquire → |
| Metric | 18 mm | 1.5 mm | Enquire → |
| Metric | 18 mm | 2.0 mm | Enquire → |
| Metric | 25 mm | 2.0 mm | Enquire → |
| Fractional | 1/4 in. | 0.035 in. | Enquire → |
| Fractional | 1/4 in. | 0.049 in. | Enquire → |
| Fractional | 3/8 in. | 0.035 in. | Enquire → |
| Fractional | 3/8 in. | 0.049 in. | Enquire → |
| Fractional | 1/2 in. | 0.035 in. | Enquire → |
| Fractional | 1/2 in. | 0.049 in. | Enquire → |
| Fractional | 1/2 in. | 0.065 in. | Enquire → |
| Fractional | 3/4 in. | 0.065 in. | Enquire → |
| Fractional | 1 in. | 0.083 in. | Enquire → |
No matching dimensions. Send your required size to Fluidline.
Metric and inch sizes are different
| Fractional outside diameter | Exact metric conversion | Do not substitute with |
|---|---|---|
| ¼″ | 6.35 mm | 6 mm fittings |
| ⅜″ | 9.525 mm | 10 mm fittings |
| ½″ | 12.7 mm | 12 mm fittings |
| ¾″ | 19.05 mm | 18 mm or 20 mm fittings |
| 1″ | 25.4 mm | 25 mm fittings |
Use a fitting designed for the actual tube outside diameter. Similar-looking metric and fractional sizes must not be treated as interchangeable.
Understanding OD, ID and wall thickness
Outside diameter (OD) is measured across the outside of the tube. Wall thickness is the metal thickness. For a nominal circular tube, inside diameter (ID) equals OD minus twice the wall thickness. Manufacturing tolerances mean the measured dimensions may differ from the nominal values.
For example, a nominal 12 mm OD × 1.5 mm wall tube has a nominal 9 mm bore. That calculation describes geometry only; it is not a pressure calculation.
Use the full tables for technical selection
Download F-Line seamless stainless steel tubing PDFSee the pressure and temperature guide for the limits and conditions that accompany reference pressure values.
Frequently asked questions
Is ½-inch tubing the same as 12 mm tubing?
No. ½ inch is exactly 12.7 mm. Use the matching fractional or metric fitting, even when the dimensions appear close.
Does a thicker wall always solve a pressure problem?
No. The fitting’s approved wall range, bore requirement, material, temperature, tolerances and system design must all be checked.