What is ASTM A194 Grade 7?
ASTM A194 Grade 7 is a standard material specification for high-tensile nuts and other internally threaded fasteners manufactured from chromium-molybdenum alloy steel specifically AISI 4140, 4142, 4145, 4140H, 4142H and 4145H. The nuts are produced by hot forging, cold forging or machining from bar stock and are subsequently quenched and tempered to achieve a Brinell hardness of 248–327 BHN.
The industry standard for B7 bolting: ASTM A194 Grade 7 nuts are the premier alloy steel companion nut for ASTM A193 Grade B7 stud bolts. The Cr-Mo alloy composition delivers higher proof loads, better elevated-temperature retention, and NACE MR0175 sour-service compliance advantages that Grade 2H medium-carbon nuts cannot match.
Grade 7 nuts find widespread use in bolted flange joints for pressure vessels, heat exchangers, pipelines, valves and other critical industrial equipment. The ASME SA194 Grade 7 designation is technically equivalent to ASTM A194 Grade 7 and is used where ASME Boiler & Pressure Vessel Code certification is required. Jade Alloys supplies dual-certified A194/SA194 Grade 7 nuts with full 3.1 Mill Test Certificates from its Mumbai manufacturing facility.
ASTM Update — Grade 4 Discontinued: In 2017, ASTM formally removed Grade 4 nuts from the A194 specification. Grade 7 is the designated replacement. If your specifications still reference A194 Grade 4, Grade 7 is the correct current equivalent.
A194 Grade 7 vs. Grade 2H — Key Differences
| Material | Medium Carbon Steel |
| Hardness | 248–341 BHN |
| NACE MR0175 | No |
| Cr-Mo Alloy | No |
| Sour service | Not suitable |
| Common pairing | A193 B7 (general) |
| Material | Cr-Mo Alloy Steel |
| Hardness | 248–327 BHN |
| NACE MR0175 | Yes (≤22 HRC) |
| Cr-Mo Alloy | Yes (AISI 4140/4145H) |
| Sour service | Suitable |
| Common pairing | A193 B7 (demanding service) |
Chemical Composition of ASTM A194 Grade 7 Nuts
ASTM A194 Grade 7 nuts are produced from chromium-molybdenum alloy steels primarily AISI 4140, 4142, 4145, and their H-band equivalents. The presence of chromium distinguishes Grade 7 from the now-discontinued Grade 4.
Grade 7 Chemical Composition (per ASTM A194)
| Element | Carbon (C) % | Manganese (Mn) % | Phosphorus (P) % max | Sulfur (S) % max | Silicon (Si) % | Chromium (Cr) % | Molybdenum (Mo) % |
|---|---|---|---|---|---|---|---|
| Range | 0.37–0.49 | 0.65–1.10 | 0.035 | 0.040 | 0.15–0.35 | 0.75–1.20 | 0.15–0.25 |
| Product Var. (±) | 0.02 | 0.04 | 0.005 over | 0.005 over | 0.02 | 0.05 | 0.02 |
Note: The intentional addition of Bi, Se, Te, and Pb is not permitted. For bar stock over 90 mm (3½″), carbon content may reach 0.50% max.
Grade 7 vs. Grade 4 — Chemical Comparison
| Grade | Carbon (C) % | Manganese (Mn) % | Chromium (Cr) % | Molybdenum (Mo) % | Status |
|---|---|---|---|---|---|
| A194 Grade 4 | 0.40–0.50 | 0.70–0.90 | None | 0.20–0.30 | Discontinued (2017) |
| A194 Grade 7 | 0.37–0.49 | 0.65–1.10 | 0.75–1.20 | 0.15–0.25 | Current Standard |
Mechanical Properties & Hardness
ASTM A194 Grade 7 nuts are governed by hardness requirements rather than tensile strength. Proof load requirements are specified per nominal size and nut type.
Hardness Requirements
| Grade | Brinell (BHN) — Completed Nuts | Rockwell HRC — Completed Nuts | Min. BHN After Heat Treatment (Sample) | Min. HRB After Heat Treatment (Sample) |
|---|---|---|---|---|
| Grade 7 | 248–327 | 24–35 | 201 | 94 |
Heat treatment: Grade 7 shall be quenched and tempered at a minimum temperature of 595°C (1100°F). NACE MR0175 compliance requires hardness ≤22 HRC (238 HBN) for sour service applications.
Proof Load — Heavy Hex Nuts (Inch Series)
| Nominal Size (in) | Threads Per Inch | Proof Load — Heavy Hex (lbf) | Proof Load — Hex (lbf) | Proof Stress — Heavy Hex (psi) |
|---|---|---|---|---|
| ¼″ | 20 | 5,570 | 4,770 | 175,000 |
| ⅜″ | 16 | 13,560 | 11,620 | 175,000 |
| ½″ | 13 | 24,830 | 21,280 | 175,000 |
| ⅝″ | 11 | 39,550 | 33,900 | 175,000 |
| ¾″ | 10 | 58,450 | 50,100 | 175,000 |
| ⅞″ | 9 | 80,850 | 69,300 | 175,000 |
| 1″ | 8 | 106,000 | 90,900 | 175,000 |
| 1¼″ | 8 | 175,000 | 150,000 | 175,000 |
| 1½″ | 8 | 261,100 | 223,800 | 175,000 |
Heavy hex proof stress: 175,000 psi. Standard hex proof stress: 150,000 psi. Full proof load tables per ASTM A194 are available on request.
Grade 7 vs. Grade 7M — Comparison
| Property | Grade 7 | Grade 7M |
|---|---|---|
| Material | AISI 4140/4145H | AISI 4140/4145H |
| Hardness (BHN) | 248–327 | 159–229 |
| Hardness (HRC) | 24–35 | — |
| Application | High-pressure, high-temp service | NACE sour service (controlled hardness) |
| NACE MR0175 | Only at ≤22 HRC | Yes (designed for compliance) |
Specification & Supply Parameters
Jade Alloys manufactures and supplies ASTM A194 Grade 7 nuts to the following parameters. Custom sizes, coatings, and certifications are available on request.
| Parameter | Details |
|---|---|
| Specification | ASTM A194 / ASME SA194 Grade 7 (dual certified) |
| Material Grades | AISI 4140, 4142, 4145, 4140H, 4142H, 4145H |
| Dimension Standard (Inch) | ASME B18.2.2 (hex), ASME B18.2.2 (heavy hex) |
| Dimension Standard (Metric) | ASME B18.2.4.1M, ASME B18.2.4.2M |
| Thread Standard | ASME B1.1 (Unified Inch) / ASME B1.13M (Metric Coarse) |
| Size Range — Inch | ¼″ to 4″ (UNC/UNF) |
| Size Range — Metric | M6 to M100 |
| Heat Treatment | Quenched & Tempered — minimum tempering at 595°C (1100°F) |
| Hardness | 248–327 BHN / 24–35 HRC (completed nuts) |
| NACE Compliance | MR0175 / ISO 15156 (at ≤22 HRC / 238 BHN) |
| Additional Compliance | PED 97/23/EC; ASME BPVC; ISO 15156 |
| Marking | Hot/cold forged: “7”; Machined from bar: “7B” |
| Finish / Coating | Plain, Hot-Dip Galvanized (ASTM A153), Black Oxide, Xylan, PTFE, Zinc Nickel |
| Certification | EN 10204 Type 3.1 MTC; NABL-approved lab reports |
Available Product Types
Jade Alloys manufactures ASTM A194 Grade 7 fasteners in all standard nut and threaded forms. Custom configurations are produced to drawing.
All Grade 7 nut types are available with matching ASTM A193 B7 stud bolts and ASTM F436 Type 1 hardened washers as complete bolting sets ideal for flanged piping, pressure vessel, and heat exchanger applications.
Dimension Chart of ASTM A194 Grade 7 Heavy Hex Nuts
Standard dimensions for ASTM A194 Grade 7 Heavy Hex Nuts per ASME B18.2.2 (inch) and ASME B18.2.4.2M (metric). Contact Jade Alloys for non-standard sizes or custom configurations.
Inch Series — Heavy Hex Nut Dimensions (ASME B18.2.2)
| Nominal Size (in) | TPI (UNC) | Width Across Flats (in) | Width Across Corners (in) | Thickness (in) | Bearing Face Dia. (in) |
|---|---|---|---|---|---|
| ½″ | 13 | ⅞ | 1.010 | 31/64 | 0.902 |
| ⅝″ | 11 | 1-1/16 | 1.227 | 39/64 | 1.085 |
| ¾″ | 10 | 1-¼ | 1.443 | 47/64 | 1.269 |
| ⅞″ | 9 | 1-7/16 | 1.660 | 55/64 | 1.453 |
| 1″ | 8 | 1-⅝ | 1.876 | 63/64 | 1.638 |
| 1-⅛″ | 8 | 1-13/16 | 2.093 | 1-7/64 | 1.825 |
| 1-¼″ | 8 | 2 | 2.309 | 1-7/32 | 2.010 |
| 1-⅜″ | 8 | 2-3/16 | 2.526 | 1-11/32 | 2.197 |
| 1-½″ | 8 | 2-⅜ | 2.742 | 1-31/64 | 2.385 |
| 1-¾″ | 5 | 2-¾ | 3.175 | 1-43/64 | 2.760 |
| 2″ | 4.5 | 3-⅛ | 3.608 | 1-⅞ | 3.135 |
| 2-½″ | 4 | 3-⅞ | 4.474 | 2-5/16 | 3.885 |
| 3″ | 4 | 4-⅝ | 5.341 | 2-¾ | 4.635 |
| 4″ | 4 | 6-⅛ | 7.073 | 3-⅝ | 6.135 |
Metric Series — Heavy Hex Nut Dimensions (ASME B18.2.4.2M)
| Nominal Size (mm) | Thread Pitch (mm) | Width Across Flats (mm) | Width Across Corners (mm) | Thickness (mm) |
|---|---|---|---|---|
| M10 | 1.5 | 17 | 19.6 | 9.3 |
| M12 | 1.75 | 21 | 24.2 | 11.1 |
| M16 | 2.0 | 27 | 31.2 | 14.8 |
| M20 | 2.5 | 34 | 39.3 | 18.7 |
| M24 | 3.0 | 41 | 47.3 | 22.5 |
| M30 | 3.5 | 50 | 57.7 | 27.7 |
| M36 | 4.0 | 60 | 69.3 | 33.0 |
| M42 | 4.5 | 70 | 80.8 | 38.5 |
| M48 | 5.0 | 80 | 92.4 | 44.0 |
| M56 | 5.5 | 90 | 103.9 | 50.3 |
| M64 | 6.0 | 100 | 115.5 | 57.5 |
| M80 | 6.0 | 125 | 144.3 | 72.0 |
| M100 | 6.0 | 155 | 179.0 | 90.0 |
Dimensions are indicative per ASME B18.2.2 / B18.2.4.2M. Non-standard sizes and custom configurations are supplied per customer drawing. Contact Jade Alloys for exact dimensional data.
ASTM A194 Nut Grades
ASTM A194 covers multiple nut grades for different bolting applications. Jade Alloys manufactures the full range.
Recommended Mating Hardware & Bolt Compatibility
For code-compliant bolted joints, pair ASTM A194 Grade 7 nuts with the following certified hardware. Jade Alloys supplies matched bolting sets with combined MTC documentation.
| Component | Specification | Application Notes |
|---|---|---|
| Primary Bolt | ASTM A193 Grade B7 | Standard pairing for high-pressure, high-temperature flanged joints |
| Alternative Bolt (elevated temp.) | ASTM A193 Grade B16 | Where service exceeds 370°C and Grade 16 nut is not specified |
| Washers | ASTM F436 Type 1 | Hardened circular washers for structural and pressure vessel use |
| Flange Standard | ASME B16.5 / B16.47 | Class 150 to Class 2500 flanged joints |
Complete bolting sets available: Jade Alloys supplies B7 stud bolt + Grade 7 heavy hex nut + F436 washer sets for flanged piping and pressure vessel assembly. Single MTC covering all components supplied on request.
International Grade Equivalents
ASTM A194 Grade 7 chromium-molybdenum alloy steel nuts are recognised under several international standards. Specify the exact standard with your order.
Equivalency is approximate. Always verify against the applicable project specification before substitution. Jade Alloys can provide cross-certification documentation on request.
Testing, Certifications & Quality
Every batch of ASTM A194 Grade 7 nuts from Jade Alloys undergoes rigorous quality testing. All certifications are furnished with the delivery.
Testing Conducted
| Test Type | Method / Standard | Parameter Verified |
|---|---|---|
| Chemical Analysis | Spectroscopic (OES) | Full elemental composition per A194 |
| Hardness Testing | Brinell / Rockwell (HRC) | 248–327 BHN; ≤22 HRC for NACE |
| Proof Load Testing | ASTM A194 — per size | Heavy hex and hex proof loads |
| Dimensional Inspection | ASME B18.2.2 / B18.2.4.2M | Across flats, thickness, bearing face |
| Visual & Surface Inspection | ASTM A194 | Surface condition, thread integrity |
| Impact Testing (Grade 7L) | Charpy V-notch at -101°C | Low-temperature toughness |
| Hydrogen-Induced Cracking (on request) | NACE TM0177 / TM0284 | Sour service fitness |
Certifications Available
Industries & Applications of ASTM A194 Grade 7 Nuts
Typical Bolted Connection Applications
Grade 7 nuts are most commonly found in ASME B16.5 and B16.47 flanged connections — securing pipe flanges, valve bonnets, pressure vessel covers, heat exchanger channel heads, and turbine casings. In the oil and gas sector, their NACE MR0175 compliance makes them the standard specification for sour service wellhead and pipeline equipment. In power generation, they are used on steam boilers, condenser water boxes, and feedwater heater connections.
Why Choose Jade Alloys?
As a Mumbai-based ISO 9001:2015 certified manufacturer, Jade Alloys has supplied ASTM A194 Grade 7 nuts to engineering projects across 40+ countries. Here is what sets us apart.
Export Destinations
Jade Alloys regularly exports ASTM A194 Grade 7 nuts and bolting hardware to the following countries and regions.
Frequently Asked Questions About ASTM A194 Grade 7 Nuts
What is ASTM A194 Grade 7?
What is the hardness of ASTM A194 Grade 7 nuts?
Which bolt grade pairs with ASTM A194 Grade 7 nuts?
What is the difference between Grade 7 and Grade 2H?
What is the difference between Grade 7 and Grade 7L?
Why was ASTM A194 Grade 4 discontinued?
Are ASTM A194 Grade 7 nuts NACE MR0175 compliant?
What is the ASME equivalent of ASTM A194 Grade 7?
What coatings are available for Grade 7 nuts?
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