European wind projects default to EN 14399; North American projects specify ASTM A490. These are not interchangeable — differences in thread pitch, proof load, and coating requirements mean mixing standards on a single flange creates undefined risk.
§ 01 Standard Scope and Structure
EN 14399 is a multi-part European standard covering high-strength structural bolting assemblies for preloading. It comprises 10 sub-parts: EN 14399-1 (general requirements), EN 14399-3 (HR system — hex bolts), EN 14399-4 (HV system — hex bolts, slightly different nut geometry), EN 14399-6 (plain washers), and EN 14399-10 (HRC system — bolt with direct tension indicator). The system is CE-marked under ETA schemes and is the default for structures designed to EN 1993 (Eurocode 3).
ASTM A490 covers heat-treated steel structural bolts with a minimum tensile strength of 150 ksi (1035 MPa) for diameters up to 1½ inch. It is used alongside AISC 360 connection design and requires ASTM F3125 washers. ASTM A490 bolts are not permitted for galvanized applications — a restriction with significant consequences for offshore wind foundations.
§ 02 Mechanical Properties Compared
| Property | EN 14399 / 10.9 | ASTM A490 Type 1 | Note |
|---|---|---|---|
| Min. tensile strength | 1040 MPa | 1035 MPa (150 ksi) | Effectively equal at M24+ |
| Min. yield (0.2% proof) | 940 MPa | 895 MPa (130 ksi) | EN slightly higher |
| Min. elongation | 9% | 14% | A490 more ductile in spec |
| Hardness (Rockwell C) | 33–39 HRC | 33–38 HRC | Nearly identical range |
| Min. preload (M24) | 257 kN (HR) | ~240 kN (1" A490) | Different diameter mapping |
| Hydrogen embrittlement risk | Low (controlled process) | Prohibited with HDG | Critical for offshore use |
§ 03 Geometry and Thread Differences
This is where direct substitution fails. EN 14399 bolts use ISO metric threads (M20, M24, M30, M36…) with coarse pitch (e.g., M24×3.0 mm). ASTM A490 uses Unified National Coarse (UNC) threads in inch sizes (¾", 1", 1¼", 1½"). There is no metric-to-inch conversion that preserves thread engagement, hole tolerance, or torque coefficient simultaneously.
Flange hole patterns designed to EN 1090 (execution of steel structures) use ISO tolerance H12 clearance holes sized for metric bolts. Trying to insert an inch-diameter A490 into a metric hole, or vice versa, will result in either a loose fit (increased shear eccentricity) or an impossible fit. Never substitute across thread systems.
§ 04 Coating and Corrosion Protection
ASTM A490 explicitly prohibits hot-dip galvanizing (HDG) in its standard due to hydrogen embrittlement risk at the 150 ksi strength level. This makes it unsuitable for corrosive environments — most onshore foundations and all offshore work. ASTM A490 is typically supplied plain (oiled) or with a light phosphate coating for interior structural connections.
EN 14399 / 10.9 bolts permit HDG when the manufacturer has validated the process per EN ISO 10684, with rethreading of the nut after galvanizing to restore fit. They also permit zinc-flake coatings (Geomet, Dacromet) per ISO 10683, which are the preferred option for wind turbine tower bolts — no hydrogen risk, and corrosion performance exceeds HDG in salt-spray testing. See HDG vs Zinc-Flake Coatings for a full comparison.
§ 05 Which Standard to Specify for Wind Projects
For wind turbine towers, tower-to-foundation interfaces, and nacelle frames built to IEC 61400-1 and designed to EN 1993/EN 1090, specify EN 14399-3 HR or EN 14399-4 HV with property class 10.9. Require CE marking, EN ISO 10683 zinc-flake coating, and EN 10204 3.1 material certificates.
For North American projects using AISC design and OSHA regulatory frameworks, ASTM F3125 Grade A490 remains the standard — but only in dry, interior steel connections. For foundation anchor bolt applications (which are exposed), ASTM F1554 Grade 105 with HDG finish is more appropriate than A490. See also Grade 10.9 vs 12.9 Bolts in Wind Applications to understand why 12.9 is rarely specified despite higher strength.