Wide-Profile Inch-Series Hex Nuts for Superior Load Distribution in High-Pressure Flange and Structural Bolting.
ASME B18.2.2 Heavy Hex Nuts are inch-series internally threaded fasteners with a significantly wider and taller profile compared to standard ASME B18.2.2 regular hex nuts, providing a larger bearing surface area that distributes bolt clamping load across a wider footprint, reducing surface pressure on the flange face and minimizing the risk of nut embedment into the joint material under high preload conditions, which makes them the standard nut type for heavy hex stud bolts and heavy hex bolts used in pipe flange assemblies, pressure vessel cover connections, structural steel joints, and heavy industrial equipment connections. The ASME B18.2.2 standard defines precise dimensional requirements for heavy hex nuts including width across flats, width across corners, nut thickness, chamfer, and thread specifications for nominal sizes from 1/4 inch through 4 inches, with the heavy hex nut's wider across-flats dimension clearly distinguished from the regular hex nut to prevent dimensional mismatch in wrench and socket selection during bolted joint assembly. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, ASME B18.2.2 Heavy Hex Nuts provide the combination of wide bearing surface, superior corrosion resistance, and maintained mechanical strength that is required for offshore oil and gas flange bolting, LNG terminal pressure equipment, desalination plant pipework, marine structural steelwork, and chemical process heat exchanger covers where both the heavy hex nut geometry and stainless steel material performance are simultaneously mandated by the engineering design specification. In assemblies involving softer flange materials , such as aluminium alloy, fibre-reinforced plastic, or copper-nickel, the larger bearing area of the heavy hex nut is especially critical in preventing long-term embedment that would reduce bolt preload and lead to gasket leakage in service. ASTM A1082 heavy hex nuts are available with EN 10204 Type 3.1 material documentation for all quality-critical bolting procurement requirements.
| Nominal Size | Basic Major Diameter | Width Across Flats, F | Width Across Corners, G | Thickness, H | Maximum Runout of Bearing Surface to Thread Axis, FIM | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Basic | Min. | Max. | Min. | Max. | Basic | Min. | Max. | Up to 150k psi | 150k psi + | ||
| 1/4 | 0.2500 | 1/2 | 0.488 | 0.500 | 0.556 | 0.577 | 15/64 | 0.218 | 0.250 | 0.017 | 0.011 |
| 5/16 | 0.3125 | 9/16 | 0.546 | 0.562 | 0.622 | 0.650 | 19/64 | 0.280 | 0.314 | 0.020 | 0.012 |
| 3/8 | 0.3750 | 11/16 | 0.669 | 0.688 | 0.763 | 0.794 | 23/64 | 0.341 | 0.377 | 0.021 | 0.014 |
| 7/16 | 0.4375 | 3/4 | 0.728 | 0.750 | 0.830 | 0.866 | 27/64 | 0.403 | 0.441 | 0.022 | 0.015 |
| 1/2 | 0.5000 | 7/8 | 0.850 | 0.875 | 0.969 | 1.010 | 31/64 | 0.464 | 0.504 | 0.023 | 0.016 |
| 9/16 | 0.5625 | 15/16 | 0.909 | 0.938 | 1.037 | 1.083 | 35/64 | 0.526 | 0.568 | 0.024 | 0.017 |
| 5/8 | 0.6250 | 1 1/16 | 1.031 | 1.062 | 1.175 | 1.227 | 39/64 | 0.587 | 0.631 | 0.025 | 0.018 |
| 3/4 | 0.7500 | 1 1/4 | 1.212 | 1.250 | 1.382 | 1.443 | 47/64 | 0.710 | 0.758 | 0.027 | 0.020 |
| 7/8 | 0.8750 | 1 7/16 | 1.394 | 1.438 | 1.589 | 1.660 | 55/64 | 0.833 | 0.885 | 0.029 | 0.022 |
| 1 | 1.0000 | 1 5/8 | 1.575 | 1.625 | 1.796 | 1.876 | 63/64 | 0.956 | 1.012 | 0.031 | 0.024 |
| 1 1/8 | 1.1250 | 1 13/16 | 1.756 | 1.812 | 2.002 | 2.093 | 1 7/64 | 1.079 | 1.139 | 0.033 | 0.027 |
| 1 1/4 | 1.2500 | 2 | 1.938 | 2.000 | 2.209 | 2.309 | 1 7/32 | 1.187 | 1.251 | 0.035 | 0.030 |
| 1 3/8 | 1.3750 | 2 3/16 | 2.119 | 2.188 | 2.416 | 2.526 | 1 11/32 | 1.310 | 1.378 | 0.038 | 0.033 |
| 1 1/2 | 1.5000 | 2 3/8 | 2.300 | 2.375 | 2.622 | 2.742 | 1 15/32 | 1.433 | 1.505 | 0.041 | 0.036 |
| 1 5/8 | 1.6250 | 2 9/16 | 2.481 | 2.562 | 2.828 | 2.959 | 1 19/32 | 1.556 | 1.632 | 0.044 | 0.038 |
| 1 3/4 | 1.7500 | 2 3/4 | 2.662 | 2.750 | 3.035 | 3.175 | 1 23/32 | 1.679 | 1.759 | 0.048 | 0.041 |
| 1 7/8 | 1.8750 | 2 15/16 | 2.844 | 2.938 | 3.242 | 3.392 | 1 27/32 | 1.802 | 1.886 | 0.051 | 0.044 |
| 2 | 2.0000 | 3 1/8 | 3.025 | 3.125 | 3.449 | 3.608 | 1 31/32 | 1.925 | 2.013 | 0.055 | 0.047 |
| 2 1/4 | 2.2500 | 3 1/2 | 3.388 | 3.500 | 3.862 | 4.041 | 2 13/64 | 2.155 | 2.251 | 0.061 | 0.052 |
| 2 1/2 | 2.5000 | 3 7/8 | 3.750 | 3.875 | 4.275 | 4.474 | 2 29/64 | 2.401 | 2.505 | 0.068 | 0.058 |
| 2 3/4 | 2.7500 | 4 1/4 | 4.112 | 4.250 | 4.688 | 4.907 | 2 45/64 | 2.647 | 2.759 | 0.074 | 0.064 |
| 3 | 3.0000 | 4 5/8 | 4.475 | 4.625 | 5.102 | 5.340 | 2 61/64 | 2.893 | 3.013 | 0.081 | 0.070 |
| 3 1/4 | 3.2500 | 5 | 4.838 | 5.000 | 5.515 | 5.774 | 3 3/16 | 3.124 | 3.252 | 0.087 | 0.075 |
| 3 1/2 | 3.5000 | 5 3/8 | 5.200 | 5.375 | 5.928 | 6.207 | 3 7/16 | 3.370 | 3.506 | 0.094 | 0.081 |
| 3 3/4 | 3.7500 | 5 3/4 | 5.562 | 5.750 | 6.341 | 6.640 | 3 11/16 | 3.616 | 3.760 | 0.100 | 0.087 |
| 4 | 4.0000 | 6 1/8 | 5.925 | 6.125 | 6.755 | 7.073 | 3 15/16 | 3.862 | 4.014 | 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).
