Wide-Profile Metric Nuts for Superior Load Distribution in High-Pressure and Heavy Structural Bolted Assemblies.
ASME B18.2.4.6M Metric Heavy Hex Nuts are metric-series internally threaded fasteners featuring a significantly wider and taller profile compared to standard ASME B18.2.4.1M metric hex nuts, providing a greater bearing surface area that distributes clamping load across a larger footprint, reducing the risk of embedment into flange or structural steel bearing surfaces under high bolt preload. ASME B18.2.4.6M defines precise metric dimensions for width across flats, width across corners, nut height, bearing face diameter, and 6H metric coarse thread tolerances for sizes M12 through M100, ensuring dimensional interchangeability between heavy hex nut suppliers on global metric-standard projects. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, these metric heavy hex nuts provide the combination of wide bearing surface, superior corrosion resistance, and maintained mechanical performance required for offshore structure flange bolting, LNG plant pressure equipment, desalination plant piping, and marine infrastructure assemblies. In applications involving softer flange materials such as aluminium, GRP, or duplex stainless steel, the larger bearing area of the heavy hex nut is particularly critical in preventing nut face embedment that would reduce bolt preload and compromise gasket seating stress over time. ASTM A1082 metric heavy hex nuts are supplied with EN 10204 Type 3.1 material certificates for all quality-controlled project requirements.
| Nominal Dia. | Width Across Flats, S | Width Across Corners, E | Thickness, M | Bearing Face Dia., Dw | Washer Face Thickness, C | Total Runout of Bearing Surface FIM | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Max. | Min. | Max. | Min. | Min. | Max. | Min. | Max. | |
| M12 | 21.00 | 20.16 | 24.25 | 22.78 | 12.3 | 11.9 | 19.2 | 0.8 | 0.4 | 0.38 |
| M14 | 24.00 | 23.16 | 27.71 | 26.17 | 14.3 | 13.6 | 22.0 | 0.8 | 0.4 | 0.42 |
| M16 | 27.00 | 26.16 | 31.18 | 29.56 | 17.1 | 16.4 | 24.9 | 0.8 | 0.4 | 0.47 |
| M20 | 34.00 | 33.00 | 39.26 | 37.29 | 20.7 | 19.4 | 31.4 | 0.8 | 0.4 | 0.58 |
| M22 | 36.00 | 35.00 | 41.57 | 39.55 | 23.6 | 22.3 | 33.3 | 0.8 | 0.4 | 0.63 |
| M24 | 41.00 | 40.00 | 47.34 | 45.20 | 24.2 | 22.9 | 38.0 | 0.8 | 0.4 | 0.72 |
| M27 | 46.00 | 45.00 | 53.12 | 50.85 | 27.5 | 26.3 | 42.8 | 0.8 | 0.4 | 0.80 |
| M30 | 50.00 | 49.00 | 57.74 | 55.37 | 30.7 | 29.1 | 45.6 | 0.8 | 0.4 | 0.87 |
| M36 | 60.00 | 58.80 | 69.28 | 66.44 | 36.6 | 35.0 | 55.9 | 0.8 | 0.4 | 1.05 |
| M42 | 70.00 | 67.90 | 80.83 | 77.41 | 42.0 | 40.4 | 64.5 | 1.0 | 0.5 | 1.22 |
| M48 | 80.00 | 77.60 | 92.38 | 88.46 | 48.0 | 46.4 | 73.7 | 1.0 | 0.5 | 1.40 |
| M56 | 90.00 | 87.20 | 103.92 | 99.41 | 56.0 | 54.1 | 82.8 | 1.0 | 0.5 | 1.57 |
| M64 | 100.00 | 96.80 | 115.47 | 110.35 | 64.0 | 62.1 | 92.0 | 1.0 | 0.5 | 1.75 |
| M72 | 110.00 | 106.40 | 127.02 | 121.30 | 72.0 | 70.1 | 101.1 | 1.2 | 0.6 | 1.92 |
| M80 | 120.00 | 116.00 | 138.56 | 132.24 | 80.0 | 78.1 | 110.2 | 1.2 | 0.6 | 2.09 |
| M90 | 135.00 | 130.50 | 155.88 | 148.77 | 90.0 | 87.8 | 124.0 | 1.2 | 0.6 | 2.36 |
| M100 | 150.00 | 145.00 | 173.21 | 165.30 | 100.0 | 97.8 | 137.8 | 1.2 | 0.6 | 2.62 |
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 B18.2.4.6M, 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).
