ASTM F3125 GRADE A490 HIGH-STRENGTH STRUCTURAL BOLTING — TECHNICAL DATASHEET

Historically governed under a standalone specification, ASTM A490 and A490M have been consolidated under the unified standard ASTM F3125 / F3125M. Designated as ASTM F3125 Grade A490 (Imperial) and Grade A490M (Metric), this standard covers quenched and tempered alloy steel heavy hex structural bolts with a minimum tensile strength of 150 ksi (1040 MPa).

Grade A490 is specifically engineered for heavy civil infrastructure, bridges, and high-rise buildings requiring the highest structural tensile strength. The consolidation standardized a uniform tensile strength requirement across all specified diameters ranging from 1/2 in. to 1-1/2 in. (M12 to M36 in metric), ensuring consistent load-bearing capacities without the historical strength step-downs of larger cross-sections.

■ Material Classifications and Connection Types

Grade A490 bolts are categorized by material chemistry and are approved for specific structural connection interfaces:

Type 1: High-strength alloy steel or alloy steel with boron additions. Standard for general-purpose, high-load steel-to-steel connections.
Type 2: Low-carbon martensitic steel (Officially withdrawn in 2002).
Type 3: Weathering steel, possessing inherent atmospheric corrosion resistance (Corrosion Index $I \ge 6.0$). Forms a protective oxide patina, minimizing the need for protective paint.
SC (Slip-Critical): Shear load is transferred entirely by friction between faying surfaces. Requires high, reliable installation preload.
Type N & Type X: Bearing-type connections with threads included in the shear plane (N) or excluded from the shear plane (X).

■ Chemical Composition Limits

Rigorous control over alloying elements ensures complete hardenability (full martensitic conversion) during heat treatment.

Element	Type 1 Heat Analysis (%)	Type 1 Product Analysis (%)	Type 3 Heat Analysis (%)	Type 3 Product Analysis (%)
Carbon (Sizes ≤ 1-3/8 in.)	0.30 – 0.48	0.28 – 0.50	0.30 – 0.53 max	0.28 – 0.55 max
Carbon (Size = 1-1/2 in.)	0.35 – 0.53	0.33 – 0.55	0.30 – 0.53 max	0.28 – 0.55 max
Manganese (Min)	0.60	0.57	0.60	0.57
Phosphorus (Max)	0.035	0.040	0.035	0.040
Sulfur (Max)	0.040	0.045	0.040	0.045
Copper	Not Specified	Not Specified	0.20 – 0.60	0.17 – 0.63
Chromium (Min)	Not Specified	Not Specified	0.45	0.42
Nickel (Min)*	Not Specified	Not Specified	0.20	0.17
Molybdenum (Min)*	Not Specified	Not Specified	0.10	0.09
Boron (Max)	0.003	0.003	Not Specified	Not Specified

* For Type 3 weathering steel, either Nickel or Molybdenum must be present in the specified minimum quantity.

■ Proprietary Datasheet Download

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ASTM F3125 Grade A490 — Complete Technical Yield & Tolerance Datasheet

Contains empirical data for stress simulations, slip-critical tension tables, and advanced coating guidelines. Corporate/engineering credentials required.

⬇ DOWNLOAD DATASHEET

■ Mechanical Properties and Hardness

Grade A490 bolts require a precise oil quenching and tempering sequence (tempered at no less than 800°F / 427°C) to guarantee high yield strength and adequate ductility.

Property / Specification	Imperial (1/2 to 1-1/2 in. Inclusive)	Metric (M12 to M36 Inclusive)
Tensile Strength (Range / Min)	150 – 173 ksi	1040 – 1210 MPa
Yield Strength (Min)	130 ksi	940 MPa
Elongation in 4D (Min %)	14%	14%
Reduction of Area (Min %)	40%	40%
Hardness Range (Rockwell C)	33 to 39 HRC	33 to 39 HRC
Hardness Range (Brinell)	311 to 352 HBW	311 to 352 HBW

■ Structural Tensile and Proof Load Requirements

Thread Designation (UNC)	Stress Area (in²)	Tensile Min (lbf)	Tensile Max (lbf)	Proof Load (Length Method) (lbf)
1/2 - 13	0.142	21,300	24,600	17,050
5/8 - 11	0.226	33,900	39,100	27,100
3/4 - 10	0.334	50,100	57,800	40,100
7/8 - 9	0.462	69,300	79,950	55,450
1 - 8	0.606	90,900	104,850	72,700
1-1/8 - 7	0.763	114,450	132,000	91,550
1-1/4 - 7	0.969	145,350	167,680	116,300
1-3/8 - 6	1.155	173,250	199,850	138,600
1-1/2 - 6	1.405	210,750	243,100	168,600

■ Dimensions and Heavy Hex Geometry

Manufactured as heavy hex structural bolts (ASME B18.2.6), providing a wider across-flats profile and a larger head height to distribute high preloads over a broader bearing surface.

Nominal Dia.	Body Dia. Max	Width Across Flats Basic	Width Across Corners Min	Head Height Basic	Basic Thread Length
1/2"	0.515	7/8"	0.969	5/16"	1.00
5/8"	0.642	1-1/16"	1.175	25/64"	1.25
3/4"	0.768	1-1/4"	1.383	15/32"	1.38
7/8"	0.895	1-7/16"	1.589	35/64"	1.50
1"	1.022	1-5/8"	1.796	39/64"	1.75
1-1/4"	1.277	2"	2.209	25/32"	2.00
1-1/2"	1.531	2-3/8"	2.622	15/16"	2.25

■ Coating Restrictions & Hydrogen Embrittlement

CRITICAL RESTRICTION: Grade A490 bolts MUST NOT be hot-dip galvanized (HDG), electroplated with zinc, or coated via mechanical deposition.

This prohibition addresses two failure modes:

Hydrogen Embrittlement (HE): With strengths > 150 ksi and hardness up to 39 HRC, A490 bolts are highly susceptible to Internal Hydrogen Embrittlement (IHE) caused by acid pickling or plating operations.
Thermal Microstructural Damage: Hot-dip galvanizing baths (840°F - 860°F) exceed the minimum tempering temperature of A490 (800°F), risking in-bath annealing and a permanent reduction of mechanical properties.

Approved Coatings: ASTM F3125 permits only non-electrolytic, zinc-aluminum dispersion coatings, such as ASTM F1136 Grade 3 (Geomet), ASTM F2833 Grade 1 (Magni 565), and ASTM F3393.

■ Inspection, Quality Assurance, and Hardware Integration

Non-Destructive Testing (100% MPI): All A490 production lots must undergo 100% Magnetic Particle Inspection (MPI) per ASTM F788 to detect subsurface/surface discontinuities, seams, and transverse cracks. Fasteners also undergo decarburization/carburization evaluation (ASTM F2328).

Companion Hardware: Substituting hardware with non-compatible grades can result in joint slip or premature failure.

Fastener Type & Finish	Matching Nut Standard & Grade	Matching Washer Standard & Type
A490 Type 1 (Plain / Uncoated)	ASTM A563 Grade DH (or A194 Gr 2H)	ASTM F436 Type 1 Hardened Steel
A490 Type 1 (Coated F1136 / F2833)	ASTM A563 Grade DH (Coated to match)	ASTM F436 Type 1 (Coated to match)
A490 Type 3 (Weathering Steel)	ASTM A563 Grade DH3 Weathering	ASTM F436 Type 3 Weathering

■ Engineering Conclusions and Installation Recommendations

Absolute Prohibition of Reuse: Because Grade A490 steel is formulated with high strength and a narrow yield-to-tensile ratio, the fastener possesses limited plastic deformation reserve. Subjecting a previously tightened A490 bolt to a secondary installation risks sudden structural fracture.
Installation Validation: Pre-tensioning must be strictly monitored via the Turn-of-Nut Method, Direct Tension Indicators (DTIs), Calibrated Wrench Method, or by utilizing Twist-Off (F2280) assemblies.
Enforce Strict Thread Shear Exclusions: In high-load shear connections, design details should utilize the "X" connection configuration. Grade A490 structural bolts are designed with shorter thread lengths to keep threads out of the shear plane, ensuring the full cross-sectional area resists shear forces.