Standard Inch-Series Regular Hex Nuts for Structural, Mechanical, and Process Industry Bolted Connections.
ASME B18.2.2 Hex Nuts are the most widely used inch-series internally threaded fasteners in North American engineering, construction, and manufacturing , governing dimensional requirements for standard regular hexagonal nuts used as the primary mating nut for ASME B18.2.1 hex bolts, hex cap screws, and stud bolts across structural steel connections, mechanical assemblies, process piping, and pressure equipment applications throughout the full nominal size range from 1/4 inch through 4 inches. The ASME B18.2.2 standard defines precise dimensional requirements for regular hex nuts including width across flats, width across corners, nut thickness, bearing face, chamfer dimensions, and thread specifications, ensuring complete dimensional interchangeability across all compliant nut manufacturers and maintaining consistent clamping performance in bolted joint design calculations. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, ASME B18.2.2 Hex Nuts deliver excellent corrosion resistance and sustained mechanical performance in aggressive service environments including marine structures, chemical processing plants, coastal infrastructure, pharmaceutical manufacturing facilities, food and beverage processing buildings, and water treatment infrastructure where carbon steel hex nuts would suffer rapid surface corrosion, thread degradation, and eventual seizure under the combined effects of atmospheric moisture and chemical exposure. ASTM A1082 hex nuts per ASME B18.2.2 are the standard mating nut for ASME B18.2.1 hex bolts and cap screws in ASTM A1082 stainless steel, forming dimensionally matched and fully corrosion-resistant inch-series bolted assemblies for critical service applications. Full EN 10204 Type 3.1 material certification is available for all ASTM A1082 ASME B18.2.2 hex nut lots supplied to quality-critical projects.
| Nominal Size | Basic Major Diameter of Thread | Width Across Flats, F | Width Across Corners, G | Thickness, H |
Maximum Runout of Bearing Surface to Thread Axis, FIM |
||||
|---|---|---|---|---|---|---|---|---|---|
| Min. | Max | Min. | Max | Min. | Max | Up to 150,000 psi | 150,000 psi and Greater | ||
| 1/4 | 0.2500 | 0.428 | 0.438 | 0.488 | 0.505 | 0.212 | 0.226 | 0.015 | 0.010 |
| 5/16 | 0.3125 | 0.489 | 0.500 | 0.557 | 0.577 | 0.258 | 0.273 | 0.016 | 0.011 |
| 3/8 | 0.3750 | 0.551 | 0.563 | 0.628 | 0.650 | 0.320 | 0.337 | 0.017 | 0.012 |
| 7/16 | 0.4375 | 0.675 | 0.688 | 0.768 | 0.794 | 0.365 | 0.385 | 0.018 | 0.013 |
| 1/2 | 0.5000 | 0.736 | 0.750 | 0.840 | 0.866 | 0.427 | 0.448 | 0.019 | 0.014 |
| 9/16 | 0.5625 | 0.861 | 0.875 | 0.982 | 1.010 | 0.473 | 0.496 | 0.020 | 0.015 |
| 5/8 | 0.6250 | 0.922 | 0.938 | 1.051 | 1.083 | 0.535 | 0.559 | 0.021 | 0.016 |
| 3/4 | 0.7500 | 1.088 | 1.125 | 1.240 | 1.299 | 0.617 | 0.665 | 0.023 | 0.018 |
| 7/8 | 0.8750 | 1.269 | 1.312 | 1.447 | 1.516 | 0.724 | 0.776 | 0.025 | 0.020 |
| 1 | 1.0000 | 1.450 | 1.500 | 1.653 | 1.732 | 0.831 | 0.887 | 0.027 | 0.022 |
| 1 1/8 | 1.1250 | 1.631 | 1.688 | 1.859 | 1.949 | 0.939 | 0.999 | 0.030 | 0.025 |
| 1 1/4 | 1.2500 | 1.812 | 1.875 | 2.066 | 2.165 | 1.030 | 1.094 | 0.033 | 0.028 |
| 1 3/8 | 1.3750 | 1.994 | 2.062 | 2.273 | 2.382 | 1.138 | 1.206 | 0.036 | 0.031 |
| 1 1/2 | 1.5000 | 2.175 | 2.250 | 2.480 | 2.598 | 1.245 | 1.317 | 0.039 | 0.034 |
| 1 5/8 | 1.6250 | 2.35 | 2.43 | 2.679 | 2.805 | 1.364 | 1.416 | 0.044 | 0.038 |
| 1 3/4 | 1.7500 | 2.538 | 2.625 | 2.893 | 3.031 | 1.460 | 1.540 | 0.048 | 0.041 |
| 1 7/8 | 1.8750 | 2.722 | 2.813 | 3.103 | 3.247 | 1.567 | 1.651 | 0.051 | 0.044 |
| 2 | 2.0000 | 2.900 | 3.000 | 3.306 | 3.464 | 1.675 | 1.763 | 0.055 | 0.047 |
| 2 1/4 | 2.2500 | 3.263 | 3.375 | 3.719 | 3.897 | 1.890 | 1.986 | 0.061 | 0.052 |
| 2 1/2 | 2.5000 | 3.625 | 3.750 | 4.133 | 4.330 | 2.105 | 2.209 | 0.068 | 0.058 |
| 2 3/4 | 2.7500 | 3.988 | 4.125 | 4.546 | 4.763 | 2.319 | 2.431 | 0.074 | 0.064 |
| 3 | 3.0000 | 4.350 | 4.500 | 4.959 | 5.196 | 2.534 | 2.654 | 0.081 | 0.070 |
| 3 1/4 | 3.2500 | 4.713 | 4.875 | 5.373 | 5.629 | 2.749 | 2.877 | 0.087 | 0.075 |
| 3 1/2 | 3.5000 | 5.075 | 5.250 | 5.786 | 6.062 | 2.964 | 3.100 | 0.094 | 0.081 |
| 3 3/4 | 3.7500 | 5.438 | 5.625 | 6.199 | 6.495 | 3.178 | 3.322 | 0.100 | 0.087 |
| 4 | 4.0000 | 5.800 | 6.000 | 6.612 | 6.928 | 3.393 | 3.545 | 0.107 | 0.093 |
ASTM A1082/A1082M (2016) Table 1 lists 14 duplex (ferritic-austenitic) grades, S31100, S31260, S31803, S32101, S32202, S32205 (2205), S32304 (2304), S32506, S32550 (255), S32750 (2507), S32760, S32906, S32950 and S39277, and 5 precipitation-hardening grades, S15700 (Type 632), S17400 (Type 630), S17600 (Type 635), S17700 (Type 631) and S35500 (Type 634). Grade selection depends on design, service conditions and the mechanical properties required.
Dimensions follow ASME B18.2.2, tabulated on this page. ASTM A1082/A1082M sets chemistry (Table 1), heat treatment and mechanical properties (Tables 2 to 4) and marking (Table 5). ASTM A962/A962M general requirements also apply, and A1082 prevails where the two conflict (clause 4.1). Inch-pound units apply unless the order specifies A1082M (clause 1.4).
ISO 15156-3 Table A.24 accepts wrought duplex stainless steel for any equipment when it is solution-annealed and liquid-quenched or rapidly cooled, has 35 % to 65 % ferrite and has had no ageing heat treatment. With 30 ≤ PREN ≤ 40 and Mo ≥ 1.5 % the limit is 232 °C (450 °F) and 10 kPa (1.5 psi) H2S partial pressure; with 40 < PREN ≤ 45 it is 232 °C (450 °F) and 20 kPa (3 psi). Table A.27 accepts wrought 17-4 PH (S17400) at 33 HRC max after a double age at 620 °C (1150 °F) or a modified double age, for named wellhead, valve and subsurface components, up to 3.4 kPa (0.5 psi) H2S and pH 4.5 or above.
Two supplementary requirements apply to nuts when the purchaser specifies them. S5 requires proof load testing of nuts, with the number of tests and the proof loads agreed between purchaser and manufacturer. S6 requires cross-sectional hardness testing of nuts per ASTM A370 Annex A3, with the number of tests agreed. Certification reports chemical analysis, mechanical tests and the heat treatment method (clause 10.1).
Table 4: solution annealed at 1880 to 2060 °F [1025 to 1125 °C], water quenched. Up to and including 2 in.: tensile 116 ksi [800 MPa] and yield 80 ksi [550 MPa] min. Over 2 in.: 110 ksi [760 MPa] and 75 ksi [515 MPa] min. Elongation 15 % min and hardness 33 HRC or 310 HB max for both. The marking grade symbol is 32750 (Table 5).
