DIN 2391 and EN 10305 are both specifications for precision cold-drawn seamless steel tubes, and they are often cited interchangeably on purchase orders. While they share common ground, they are not identical — and the differences matter for hydraulic cylinder tubes where bore tolerance, mechanical properties, and surface finish directly affect cylinder performance.
DIN 2391: The German Predecessor
DIN 2391 was the German national standard for cold-drawn seamless precision steel tubes, published and maintained by DIN (Deutsches Institut fu00fcr Normung). It specified five delivery conditions: BK (cold-drawn, hard), BKW (cold-drawn, stress-relieved), BKS (cold-drawn, soft-annealed), GBK (cold-drawn, annealed), and NBK (normalized, cold-drawn). For hydraulic tubes, BK and BKS were the most commonly specified conditions, with NBK used for tubes requiring further processing.
DIN 2391 was withdrawn as an active German standard and replaced by the European harmonized EN 10305 series. However, the DIN designation persists in common usage across the global hydraulic tube market, particularly in Asia, where many tube manufacturers continue to reference “DIN 2391” in their catalogs and MTCs.
EN 10305: The European Replacement
EN 10305 is a multi-part European standard covering cold-drawn and cold-rolled precision steel tubes. Part 1 covers seamless cold-drawn tubes (the direct replacement for DIN 2391). Part 4 covers seamless cold-drawn tubes for hydraulic and pneumatic power systems specifically, adding requirements for bore tolerance, surface finish, and pressure rating that Part 1 does not address.
EN 10305-4 is the correct specification for hydraulic cylinder tubes within Europe. It defines bore tolerance grades (corresponding to ISO tolerance classes H8, H9, and H10), mandates internal surface roughness requirements, and provides pressure ratings based on outside diameter, wall thickness, and steel grade. This additional specificity makes EN 10305-4 a more complete hydraulic tube specification than either DIN 2391 or EN 10305-1.
Practical Differences
The mechanical property requirements in EN 10305 are broadly equivalent to DIN 2391 for the same delivery condition. The grade designations changed from DIN’s St-based system (St 35, St 45, St 52) to EN’s E-based system (E235, E355), but the underlying chemistry and property ranges are similar. The dimensional tolerance tables are also substantially aligned, though EN 10305 uses ISO tolerance class designations that are more granular than DIN 2391’s approach.
The practical difference that matters most is regulatory: projects within the European Economic Area must reference EN standards. A purchase order citing DIN 2391 in a CE-marked system will be flagged by notified bodies and inspectors. Outside Europe, both designations are widely accepted, but referencing EN 10305-4 for hydraulic tubes signals that the buyer understands the current specification landscape and expects the additional hydraulic-specific requirements.
What to Specify
For hydraulic cylinder tubes, specify EN 10305-4 with the applicable steel grade (E235 or E355 for most applications), delivery condition (BK for maximum strength, NBK for further honing), bore tolerance class (H8 for SRB and honed applications), and any supplementary requirements for surface finish or NDT. Reference DIN 2391 only if your project explicitly requires it for backward compatibility with existing cylinder designs or qualification records.
Ordering hydraulic tubes? Send us your specification — we supply to both EN 10305-4 and DIN 2391 with full MTCs.
Cross-Referencing for Global Procurement
For manufacturers supplying hydraulic tubes to global OEMs, dual certification to both DIN 2391 and EN 10305-4 is increasingly standard practice. A tube certified to EN 10305-4 E355+N with bore tolerance class H8 satisfies both the European regulatory requirement and the legacy DIN designation that many Asian and South American OEMs still reference on their drawings. This dual certification eliminates the need for separate production runs and inventory for nominally identical products, reducing both manufacturing cost and lead time.
When reviewing an MTC that references DIN 2391, verify that the testing scope includes the hydraulic-specific requirements (bore tolerance, surface finish, pressure rating) that EN 10305-4 mandates. A tube certified only to DIN 2391 Part 1 may meet dimensional and mechanical requirements without the additional hydraulic performance verification that Part 4 of EN 10305 provides. Global Seamless supplies all hydraulic tubes with dual-standard certification covering both dimensional and hydraulic performance requirements.