A490 Heavy Hex Structural Bolt | ASTM F3125
TheA490 heavy hex structural bolt — specified originally under ASTM A490 and now consolidated into ASTM F3125 Grade A490 — is a high-strength quenched and tempered alloy steel bolt designed exclusively for structural steel-to-steel connections. Unlike standard hex bolts that serve general machinery fastening, the A490 heavy hex bolt features a significantly larger and thicker hexagon head, providing a wider bearing face that reduces clamping stress on the connected steel plates and allows higher preload values essential for slip-critical and bearing-type bolted joints. The heavy hex geometry is the distinguishing characteristic that structural engineers and offshore platform designers rely on to identify an A490 bolt on sight.
Inmarine and offshore structural applications, A490 heavy hex bolts secure primary steelwork connections including offshore platform jacket brace nodes, topside module support framing, flare boom structural brackets, living quarter module column-to-beam joints, and shipyard crane mast bolted splices. A490 Type 1 bolts are manufactured from chromium-molybdenum alloy steel (similar to AISI 4140/4142 chemistry) and are specified for atmospheric structural connections where zinc, Dacromet, or Geomet coating provides the primary corrosion barrier. A490 Type 3 bolts are made from weathering steel (comparable to COR-TEN A/B) — the chemical composition develops a stable, self-protecting oxide patina that resists atmospheric corrosion without any applied coating, making Type 3 the preferred choice for permanently exposed offshore topside structures where coating maintenance is impractical.
OurA490 structural bolts are hot-forged to the heavy hex dimensional profile per ANSI/ASME B18.2.6, followed by full-length quench and temper heat treatment achieving a minimum tensile strength of 150 ksi (1030 MPa) with hardness in the range of HRC 33-38. Each bolt head is stamped with the manufacturer's identifying mark, the grade designation"A490", and can additionally carry the"F3125"marking per the consolidated standard. Imperial sizes from 1/2"to 1-1/2"and metric equivalents from M12 to M36 are stocked, with matching A563 DH heavy hex nuts and F436 hardened washers available as a complete structural bolting assembly. Material certification per EN 10204 3.1 and rotational capacity (RoCap) testing documentation are standard deliverables; IACS class society certification is provided for offshore structural projects.
| Product Name | A490 Heavy Hex Structural Bolt / ASTM F3125 Gr.A490 / high tensile structural bolt |
| Standard | ASTM A490 / ASTM F3125 Grade A490 / ANSI B18.2.6 (Heavy Hex) |
| Type | Type 1 (Cr-Mo Alloy Steel) / Type 3 (Weathering Steel) |
| Head Pattern | Heavy hexagon (wider & thicker than standard hex) |
| Diameter | 1/2"– 1-1/2"(M12 – M36) |
| Tensile Strength | 150 ksi (1030 MPa) minimum |
| Hardness | HRC 33 – 38 |
| Heat Treatment | Quenched & tempered (full-length) |
| Coating | Plain / HDG / Dacromet / Geomet (Type 1) / Bare (Type 3 weathering) |
| Applications | Offshore jacket, topside module, flare boom, structural splice |
| Matched Nuts & Washers | A563 DH Heavy Hex Nut + F436 Hardened Washer (optional kit) |
| Certification | EN 10204 3.1, RoCap Test, IACS (LR, DNV, BV, ABS) |
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