2H Heavy Hex Nuts: Technical Specifications and Material Data
The ASTM A194 Grade 2H Heavy Hex Nut is a high-strength, internally threaded fastener designed for use in critical bolting applications subject to elevated pressure and temperature conditions. This resource provides a comprehensive overview of the applicable material properties, mechanical requirements, and dimensional specifications that govern the performance and compliance of this component.
Material and Chemical Composition
Material
The Grade 2H nut is fabricated from a medium carbon steel that undergoes specific heat treatment to achieve its high-strength properties.
Chemical Properties
| Per ASTM A194/A194M-16 | ||||||
| Grade | Material | Carbon | Manganese | Phosphorus | Sulfur (1) | Silicon |
| % by weight | % by weight | % by weight | % by weight | % by weight | ||
| 2H | Carbon Steel | 0.40 min | 1.00 max | 0.040 max | 0.050 max | 0.04 max |
- 1. Because of the degree to which sulfur segregates, product analysis for sulfur over 0.060 % max is not technologically appropriate.
Mechanical Properties and Heat Treatment
Grade 2H nuts are quenched and tempered (Q&T).
Process: The nuts are quenched in a liquid medium from a temperature above the transformation temperature.
Tempering: They are then tempered at a minimum temperature of 850° (455°C). This controlled heat treatment is crucial for developing the required hardness and mechanical properties.
| Carbon Steel, Quenched & Tempered | Per ASTM A194/A194M-16 | |||
| Diameter | Proof Load Stress | Core Hardness | Tempering Temperature | |
| Min psi | Rockwell | Min | ||
| Min | Max | |||
| 1/4" thru 1 1/2" | 175,000 | C24 | C35 | 850F |
| Over 1 1/2" | 175,000 | C35 | 850F | |
Thread Specifications
- Thread Type: Typically produced in UNC (Unified National Coarse) or UNF (Unified National Fine) threads.
- Thread Series: For sizes 1" and larger, the 8 Thread Per Inch (8-UN) series is frequently specified, particularly for pressure vessel and flanging applications, to achieve better load distribution across the threads.
- Thread Class: Generally supplied in Class 2B thread fit (Inch series) or 6H (Metric series).
Equivalent Grades: ASTM A194 Grade 2H vs. ASTM A563 Grade DH
ASTM A194 Grade 2H nuts are often used as an acceptable equivalent to ASTM A563 Grade DH nuts in high-strength structural and pressure applications. Both grades share comparable mechanical properties, including similar proof load, hardness, and tensile strength requirements.
While Grade DH nuts are covered under ASTM A563 (typically used for structural bolting), Grade 2H nuts are specified under ASTM A194 for use in high-temperature and high-pressure service. Because their mechanical performance criteria overlap, ASTM A194 Grade 2H nuts are frequently substituted for Grade DH when approved by the project specification or engineer of record.
Head Markings
ASTM A194 Grade 2H Heavy Hex Nuts are required to have permanent markings stamped into one face to ensure traceability and verify material integrity for critical applications.
Grade Identification: The stamped "2H" indicates the nut meets all requirements of the ASTM A194 standard, including chemical composition, Quenched and Tempered heat treatment, and mechanical properties.
Manufacturer Identification: Each nut must also carry a unique trademark or registered symbol. This marking provides essential traceability, linking the fastener to its production lot and the associated Material Test Report (MTR).
These permanent markings are vital for quality assurance, on-site inspections, and confirming the correct high-strength fastener is used in high-pressure, high-temperature bolted connections.
Dimensional Specifications
| Per ASME B18.2.2-2015 | ||||||||||||
| Nominal Diameter | UNC | UNF | UN8 | F | G | H | ||||||
| Width Across Flats | Width Across Corners | Thickness | ||||||||||
| Basic | Max | Min | Max | Min | Basic | Max | Min | |||||
| 1/4 | 0.250 | 20 | 28 | 1/2 | 0.500 | 0.488 | 0.577 | 0.556 | 15/64 | 0.250 | 0.218 | |
| 5/16 | 0.313 | 18 | 24 | 9/16 | 0.562 | 0.546 | 0.650 | 0.220 | 19/64 | 0.314 | 0.280 | |
| 3/8 | 0.375 | 16 | 24 | 11/16 | 0.688 | 0.669 | 0.794 | 0.763 | 23/64 | 0.377 | 0.341 | |
| 7/16 | 0.438 | 14 | 20 | 3/4 | 0.750 | 0.728 | 0.866 | 0.830 | 27/64 | 0.441 | 0.403 | |
| 1/2 | 0.500 | 13 | 20 | 7/8 | 0.875 | 0.850 | 1.010 | 0.990 | 31/64 | 0.504 | 0.464 | |
| 9/16 | 0.563 | 12 | 18 | 15/16 | 0.938 | 0.909 | 1.083 | 1.037 | 35/64 | 0.568 | 0.526 | |
| 5/8 | 0.625 | 11 | 18 | 1 1/16 | 1.062 | 1.031 | 1.227 | 1.175 | 39/64 | 0.631 | 0.587 | |
| 3/4 | 0.750 | 10 | 16 | 1 1/4 | 1.250 | 1.212 | 1.443 | 1.382 | 47/64 | 0.758 | 0.710 | |
| 7/8 | 0.875 | 9 | 14 | 1 7/16 | 1.438 | 1.394 | 1.660 | 1.589 | 55/64 | 0.885 | 0.833 | |
| 1 | 1.000 | 8 | 14 | 1 5/8 | 1.625 | 1.575 | 1.876 | 1.796 | 63/64 | 1.012 | 0.956 | |
| 1 1/8 | 1.125 | 7 | 12 | 8 | 1 13/16 | 1.812 | 1.756 | 2.093 | 2.002 | 1 7/64 | 1.139 | 1.079 |
| 1 1/4 | 1.250 | 7 | 12 | 8 | 2 | 2.000 | 1.380 | 2.309 | 2.209 | 1 7/32 | 1.251 | 1.187 |
| 1 3/8 | 1.375 | 6 | 12 | 8 | 2 3/16 | 2.188 | 2.119 | 2.526 | 2.416 | 1 11/32 | 1.378 | 1.310 |
| 1 1/2 | 1.500 | 6 | 12 | 8 | 2 3/8 | 2.375 | 2.300 | 2.742 | 2.622 | 1 15/32 | 1.505 | 1.433 |
| 1 5/8 | 1.625 | 5 1/2 | 12 | 8 | 2 9/16 | 2.562 | 2.481 | 2.959 | 2.828 | 1 19/32 | 1.632 | 1.556 |
| 1 3/4 | 1.750 | 5 | 12 | 8 | 2 3/4 | 2.750 | 2.662 | 3.175 | 3.035 | 1 23/32 | 1.759 | 1.679 |
| 1 7/8 | 1.875 | 5 | 12 | 8 | 2 15/16 | 2.938 | 2.844 | 3.392 | 3.242 | 1 27/32 | 1.886 | 1.802 |
| 2 | 2.000 | 4 1/2 | 12 | 8 | 3 1/8 | 3.125 | 3.025 | 3.608 | 3.449 | 1 31/32 | 2.013 | 1.925 |
| 2 1/4 | 2.250 | 4 1/2 | 12 | 8 | 3 1/2 | 3.500 | 3.388 | 4.041 | 3.862 | 2 13/64 | 2.251 | 2.155 |
| 2 1/2 | 2.500 | 4 | 12 | 8 | 3 7/8 | 3.875 | 3.750 | 4.474 | 4.275 | 2 29/64 | 2.505 | 2.401 |
| 2 3/4 | 2.750 | 4 | 12 | 8 | 4 1/4 | 4.250 | 4.112 | 4.907 | 4.688 | 2 45/64 | 2.759 | 2.647 |
| 3 | 3.000 | 4 | 12 | 8 | 4 5/8 | 4.625 | 4.475 | 5.340 | 5.102 | 2 61/64 | 3.013 | 2.893 |
| 3 1/4 | 3.250 | 4 | 12 | 8 | 5 | 5.000 | 4.838 | 5.774 | 5.515 | 3 3/16 | 3.252 | 3.124 |
| 3 1/2 | 3.500 | 4 | 12 | 8 | 5 3/8 | 5.375 | 5.200 | 6.207 | 5.928 | 3 7/16 | 3.506 | 3.370 |
| 3 3/4 | 3.750 | 4 | 12 | 8 | 5 3/4 | 5.750 | 5.562 | 5.562 | 6.341 | 3 11/16 | 3.670 | 3.616 |
| 4 | 4.000 | 4 | 12 | 8 | 6 1/8 | 6.125 | 5.925 | 5.925 | 6.755 | 3 15/16 | 4.014 | 3.862 |
- All dimensions are in inches.
Your Trusted Source for 2H Heavy Hex Nuts
STS Industrial supplies a full range of ASTM A194 Grade 2H Heavy Hex Nuts, engineered for high-strength, high-temperature, and high-pressure applications. Manufactured from quenched and tempered alloy steel with complete material traceability, these nuts ensure exceptional durability, reliability, and performance in critical bolted connections. Available in a wide variety of sizes and finishes, they meet the rigorous demands of industries such as oil and gas, power generation, construction, and heavy equipment. Our technical team is available to assist with product selection to ensure proper specification, compatibility, and compliance for your application.