Precision Tube Cluster
EN 10305 Cold-Drawn Precision Tubes — tolerance classes E/H8/H9
How to buy EN 10305 precision tubes by part, grade, tolerance, delivery condition, inspection document, and hydraulic use case.
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EN 10305 is the current European precision-tube family used for cold-drawn seamless, welded, and hydraulic tubes. Buyers should specify the part number, grade such as E235 or E355, delivery condition, OD/ID and wall tolerances, bore class if honed, surface finish, and EN 10204 inspection document.
Which EN 10305 part should a buyer put on the purchase order?
Use EN 10305-1 for seamless cold-drawn precision tubes, EN 10305-2 for welded cold-drawn precision tubes, and EN 10305-4 for seamless tubes for hydraulic and pneumatic power systems. The part number prevents a supplier from quoting the wrong manufacturing route.
EN 10305 is a family, not one product. Part 1 covers seamless cold-drawn tubes for precision applications. Part 2 covers welded cold-drawn tubes. Part 3 and Part 5 cover welded sized tubes and square/rectangular precision sections. Part 4 is the key hydraulic and pneumatic power-system reference. A vague RFQ saying “EN 10305 tube” can therefore return several technically different offers.
Many Indian drawings still mention DIN 2391, DIN 1629, or ST52. In new procurement, EN 10305-1 or EN 10305-4 with E355 is usually the cleaner way to specify the same family. Do not remove old DIN language blindly if the end customer or machine builder controls the drawing. Instead, write an equivalence line: DIN 2391 ST52 or EN 10305 E355 subject to MTC and dimensional acceptance.
The part number also affects documentation and inspection expectations. Hydraulic power-system tube normally needs tighter control on ID, cleanliness, and surface condition than a general mechanical precision tube. If the tube will be honed after delivery, state who performs honing and who certifies the final bore.
How are EN 10305 grades E235 and E355 selected?
E235 is suitable for lower-strength formed or mechanical parts, while E355 is the common higher-strength choice for hydraulic barrels and loaded components. Grade selection should follow design stress, welding practice, forming requirement, and MTC values rather than only stock availability.
E235 and E355 are yield-strength-based grade names. E235 is easier to form and is common in automotive, furniture, and light mechanical precision-tube work. E355 gives higher strength and is the typical choice where older drawings call for ST52. For hydraulic cylinders, E355 in a stress-relieved condition is common because it balances strength, machinability, and availability.
A buyer should not accept a higher grade automatically. If the part needs severe bending, flaring, or swaging, a softer grade or normalized condition may be better. If the tube becomes a pressure component, the design calculation and standard must allow the selected grade. The MTC should show heat number, chemistry, tensile strength, yield strength, elongation, and delivery condition.
When substituting grade names, ask the supplier to quote both the grade and standard together. “E355” without EN 10305 part and condition is incomplete. “ST52” without MTC values can also be ambiguous because older market language is not always used consistently.
Which delivery condition is right: BK, BK+S, NBK, or GBK?
Choose BK for hard as-drawn strength, BK+S for stress-relieved hydraulic and machined parts, NBK for normalized stability and welding, and GBK for annealed softness. The correct condition depends on forming, machining, welding, and final tolerance after processing.
Delivery condition is often more important than grade when the tube will be processed after purchase. BK is hard as drawn and dimensionally accurate, but residual stress can show up during machining. BK+S is stress relieved and common for hydraulic cylinder tubes. NBK is normalized and more stable for welding or further forming. GBK is annealed and used where softness is needed.
If the next operation is honing, skiving, end boring, or port welding, discuss delivery condition before ordering. A tube that is cheap in BK condition can become expensive if it moves during machining. Conversely, buying NBK for a simple spacer or sleeve may add unnecessary cost.
The purchase order should make condition a separate line item, not a note hidden in the description. Inspection documents should repeat the condition. If a supplier offers equivalent condition names from DIN 2391, ask for a written cross-reference to EN 10305 language.
How should EN 10305 tolerances be written for OD, ID, wall, and bore finish?
Write OD, ID or wall thickness, tolerance class, straightness, surface condition, and any honed-bore H8/H9 requirement separately. EN 10305 controls precision tube dimensions, while ISO 286 describes H tolerances and ISO 4287 describes measurable roughness values.
A complete EN 10305 enquiry should not rely on nominal tube size. State the outside diameter, inside diameter or wall, length, quantity, and the tolerance class required by the drawing. If only OD x wall is specified, the ID tolerance may not be controlled enough for assemblies that locate on the bore. If only ID is critical, say so clearly.
For hydraulic barrels, add the final bore class, usually H8 or H9, and the roughness value after honing or skiving. EN 10305 can describe the tube before finishing, but the cylinder maker needs the finished bore. ISO 286 and ISO 4287 give the language for measurable tolerance and roughness acceptance.
Also state straightness and cut-end requirements. Precision tube is often cut, bored, threaded, or welded after purchase. A slightly bowed length can waste machining time even if the OD and wall are within tolerance.
Specifications
| Tolerance class | OD/ID/wall tolerances per EN 10305 order class; H8/H9 bore where finished for cylinders |
|---|---|
| OD / ID range | Typical precision stock from 6-250 mm OD; hydraulic sizes quoted by OD x ID |
| Surface finish | Bright cold drawn, phosphated/oiled, honed or skived where specified; Ra per ISO 4287 |
| Grades | E235, E355 and other EN grades subject to mill route and MTC |
| Delivery condition | BK, BK+S, NBK, GBK depending on forming, machining, and welding needs |
| Documentation | EN 10204 3.1 MTC standard for industrial procurement; TPI/3.2 on request |
Standards cited for EN 10305 Cold-Drawn Precision Tubes
Reference standards cited on this page
- DIN 2391-1:1994 — Seamless precision steel tubes — Technical delivery conditions (Deutsches Institut für Normung)
- EN 10305-1:2016 — Steel tubes for precision applications — Seamless cold-drawn tubes (European Committee for Standardization (CEN))
- EN 10305-4:2016 — Seamless cold-drawn tubes for hydraulic and pneumatic power systems (European Committee for Standardization (CEN))
- ISO 286-1:2010 — Geometrical product specifications — ISO code system for tolerances on linear sizes (International Organization for Standardization)
- ISO 4287:1997 — Surface texture — Profile method — Terms, definitions and surface texture parameters (International Organization for Standardization)
- EN 10204:2004 — Metallic products — Types of inspection documents (European Committee for Standardization (CEN))
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