ST35 Tubes – DIN 2391 St35 (1.0308) Seamless Precision Steel Tubes, BK / NBK
ASC LLP, Mumbai, supplies ST35 tubes – cold-drawn seamless precision steel tubes to DIN 2391 (today EN 10305-1 E235), in BK, BKW, BKS, GBK and NBK delivery conditions. They are available in metric OD × wall sizes, cut to length, with EN 10204 3.1 certificates. See our carbon steel tubes range.
What are ST35 Tubes?
St35 (material number 1.0308) is a low-carbon steel used for seamless cold-drawn precision tubes to DIN 2391. “St” is short for Stahl (steel), and “35” refers to the old minimum tensile class of about 35 kgf/mm². The tubes are drawn to close OD and wall tolerances with a clean, smooth bore. They are the standard choice for hydraulic and pneumatic lines, cylinders and precision mechanical parts.
DIN 2391 has been replaced by EN 10305-1, in which St35 corresponds to E235. Many buyers still order “DIN 2391 St35 NBK”, and the tubes can be certified to either designation.
ST35 vs ST35.8 – Not the Same Grade
St35 (1.0308, DIN 2391) is a precision tube grade for hydraulic and mechanical use. St35.8 (1.0305, DIN 17175, now EN 10216-2 P235GH) is a boiler and pressure tube grade with guaranteed properties at elevated temperature. Choose St35 / E235 for hydraulic lines and machine parts, and St35.8 / P235GH (or ASTM A192) for boilers.
DIN 2391 Delivery Conditions Explained
- BK (+C) – cold finished / hard: no heat treatment after the last draw; highest strength, lowest ductility.
- BKW (+LC) – cold finished / soft: a light final pass after heat treatment; some bending possible.
- BKS (+SR) – cold finished and stress relieved: good strength with improved straightness for machining.
- GBK (+A) – annealed: soft, for severe bending and forming.
- NBK (+N) – normalised: uniform structure and good ductility; the usual condition for hydraulic tubes.
The codes in brackets are the EN 10305-1 equivalents.
Applications of ST35 Tubes
- Hydraulics: high-pressure hydraulic lines with compression fittings (NBK), cylinder tubes and rods
- Pneumatics and lubrication: air lines, grease and oil lines on machines
- Automotive: shock-absorber tubes, fuel and brake lines, steering parts
- Mechanical engineering: bushings, sleeves, rollers, shafts and machined parts
- Instrumentation: gauge and impulse lines
Read more: mechanical properties of ST35 seamless tubes.
ST35 Tube Size & Weight Chart (Common Hydraulic Sizes)
| OD (mm) | Wall (mm) | ID (mm) | Weight (kg/m) |
| 6 | 1 | 4 | 0.123 |
| 8 | 1 | 6 | 0.173 |
| 10 | 1.5 | 7 | 0.314 |
| 12 | 1.5 | 9 | 0.388 |
| 15 | 2 | 11 | 0.641 |
| 16 | 2 | 12 | 0.690 |
| 18 | 2 | 14 | 0.789 |
| 20 | 2.5 | 15 | 1.079 |
| 22 | 2 | 18 | 0.986 |
| 25 | 3 | 19 | 1.628 |
| 28 | 2 | 24 | 1.282 |
| 30 | 3 | 24 | 1.997 |
| 38 | 4 | 30 | 3.354 |
| 42 | 4 | 34 | 3.748 |
| 50 | 5 | 40 | 5.549 |
Precision tubes are ordered by OD × wall in mm, not by pipe schedule. The DIN 2391 / EN 10305-1 dimension range is about 4 – 120 mm OD and 0.5 – 10 mm wall; larger sizes on request. Weights calculated for steel at 7.85 g/cm³.
DIN 2391 ST35 Mechanical Properties by Delivery Condition
| Condition | Tensile Rm (MPa) | Yield ReH (MPa) | Elongation A5 |
| BK (+C) | 480 min. | – | 6% min. |
| BKW (+LC) | 420 min. | – | 10% min. |
| BKS (+SR) | 420 min. | 315 min. | 14% min. |
| GBK (+A) | 315 min. | – | 25% min. |
| NBK (+N) | 340 – 470 | 235 min. | 25% min. |
Hardness is not specified by DIN 2391; values can be agreed on order.
ST35 Tube Specifications
| Item | Details |
| Standard | DIN 2391-1 / DIN 2391-2 (replaced by EN 10305-1) |
| Grade | St35 (1.0308) = EN 10305-1 E235 |
| Type | Seamless, cold drawn precision tube |
| Delivery condition | BK, BKW, BKS, GBK, NBK (+C, +LC, +SR, +A, +N) |
| OD tolerance (typical) | ±0.08 mm up to 30 mm OD; ±0.15 – 0.50 mm for 30 – 120 mm OD |
| Wall tolerance | ±10% (min. ±0.1 mm) |
| Length | Random 5 – 7 m or exact cut lengths |
| Surface finish | Bright; oiled, phosphated or zinc-plated on request |
| Certificate | EN 10204 3.1 |
ST35 Chemical Composition (1.0308)
| Element | St35 / E235 (%) |
| Carbon (C) | 0.17 max. |
| Silicon (Si) | 0.35 max. |
| Manganese (Mn) | 0.40 min. |
| Phosphorus (P) | 0.025 max. |
| Sulphur (S) | 0.025 max. |
| Nb / Ti / V (optional) | Nb 0.03, Ti 0.03, V 0.05 max.; total 0.05 max. |
ST35 vs ST52, ST35.8 & ASTM Equivalents
| Grade | Standard / material no. | Product | NBK / main strength (MPa) |
| St35 | DIN 2391, 1.0308 = EN 10305-1 E235 | Precision tube | 340 – 470 tensile, 235 yield |
| St52 | DIN 2391, 1.0580 = EN 10305-1 E355 | Precision tube (higher strength) | 490 – 630 tensile, 355 yield |
| St35.8 | DIN 17175, 1.0305 = EN 10216-2 P235GH | Boiler / pressure tube | 360 – 480 tensile, 235 yield |
| ASTM A179 | ASME SA179 | Heat-exchanger tube | 325 / 180 (design) |
| ASTM A519 1010 – 1020 | ASTM A519 | Seamless mechanical tube | By grade and condition |
Equivalents are similar, not identical – check the drawing or design code before substituting.
Why Buy ST35 Tubes from ASC LLP?
- Correct condition: NBK for hydraulic lines, BK / BKS for machining – stated on the 3.1 certificate.
- Dual designation: certified to DIN 2391 St35 and EN 10305-1 E235 on request.
- Related products: ST52 seamless tubes, ST52 seamless pipe and ST35 round bars.
- Clean export packing: oiled, capped and bundled or boxed.
Send OD × wall, delivery condition (e.g. NBK), length and quantity to sales@amardeepsteel.com, call 022-67439130 or contact us. See also our carbon steel range.
Frequently Asked Questions – ST35 Tubes
What is DIN 2391 St35?
DIN 2391 St35 (material number 1.0308) is a low-carbon steel for seamless cold-drawn precision tubes. It is used mainly for hydraulic and pneumatic lines and precision mechanical parts. DIN 2391 has been replaced by EN 10305-1, where the equivalent grade is E235.
What does NBK mean in St35 NBK tubes?
NBK means the tubes are normalised after the final cold draw (EN 10305-1 condition +N). NBK St35 tubes have 340–470 MPa tensile strength, 235 MPa minimum yield and 25% minimum elongation, with good ductility for bending and flaring.
What is the difference between St35 and St35.8?
St35 (1.0308, DIN 2391) is a precision tube grade for hydraulic and mechanical use. St35.8 (1.0305, DIN 17175, now EN 10216-2 P235GH) is a boiler and pressure tube grade with properties guaranteed at elevated temperature.
What is the difference between St35 and St52 tubes?
St52 (1.0580, EN 10305-1 E355) contains more manganese and has higher strength – 490–630 MPa tensile and 355 MPa yield in NBK condition – compared with 340–470 MPa and 235 MPa for St35.
What is the equivalent of St35 tube?
The current European equivalent is EN 10305-1 E235. Similar ASTM materials are A179 for heat-exchanger tubes and A519 grade 1010 or 1020 for mechanical tubing, though they are not identical.
How are ST35 tubes sized?
ST35 precision tubes are ordered by outside diameter and wall thickness in millimetres, for example 20 × 2.5 mm, not by nominal pipe size or schedule.
Global Reach
ASC LLP supplies precision tubes, pipes and fittings to hydraulic, automotive and engineering customers in the USA, Europe, the Middle East and Asia, with secure packing and full documentation. Buyers worldwide rely on our ST35 tubes for certified material and traceability.
Countries We Export To
UNITED STATES, EUROPE, UK, UAE, SAUDI ARABIA, OMAN, KUWAIT, JORDAN, QATAR, INDONESIA, MALAYSIA, BRAZIL, SPAIN, ITALY, FRANCE, GERMANY, BAHRAIN, SRI LANKA, AZERBAIJAN, AUSTRALIA, AUSTRIA, PHILIPPINES, TURKEY, RUSSIA, IRAN, IRAQ, CANADA, KOREA, JAPAN, YEMEN, FINLAND, ZIMBABWE, HUNGARY, PORTUGAL, VIETNAM, MOROCCO, THAILAND, SOUTH AFRICA, MEXICO, SINGAPORE, GREECE, KUWAIT, POLAND, NEW ZEALAND, SWEDEN, SWITZERLAND, BELGIUM, BHUTAN, BANGLADESH, TAIWAN, ROMANIA, CAMBODIA, KAZAKHSTAN, AFGHANISTAN.
