Wide-Head Metric Fasteners in SI Dimensions for High-Load Structural and Pressure Bolting on Global Projects.
ASME B18.2.3.3M Metric Heavy Hex Screws are metric-series fasteners featuring a larger hexagonal head (greater width across flats, same maximum head height) than metric hex cap screws of the same size, expressed in SI dimensions, specifically engineered for heavy-duty structural, pressure vessel, and industrial flange bolting applications on global projects where metric fastener standards are specified by engineering design codes and international procurement requirements. The ASME B18.2.3.3M standard defines all critical metric dimensions for head height, width across flats, width across corners, body diameter, thread pitch, thread length, and related tolerances, ensuring dimensional interchangeability and consistent clamping performance across all metric heavy hex screw suppliers worldwide. These metric heavy hex screws are manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, which ensures that corrosion resistance, tensile strength, and mechanical reliability of the fastener meet the demanding requirements of offshore platforms, desalination plants, LNG terminals, and coastal chemical facilities where saline atmospheric conditions accelerate corrosion attack on standard carbon steel fasteners. The larger bearing footprint of the heavy hex head reduces the risk of surface embedment in lower-strength base materials such as aluminium alloy flanges and GRP structures, maintaining bolt preload over extended service periods without the need for additional hardened washers. Specifying ASME B18.2.3.3M dimensions alongside ASTM A1082 material requirements provides a complete, globally recognized definition for metric heavy hex screw procurement.
| Nominal Dia., D ,andThreadPitch | Body Diameter.,D s | Width Across Flats,S | Width Across Corners, E | Head Height, K | Wrenching Height, K 1 | Washer Face Thickness,C | Washer FaceDia.,D w | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | Min | Max | Min | Min | Max | Min | Min | |
| M12 × 1.75 | 12 | 11.73 | 21 | 20.67 | 24.25 | 23.35 | 7.76 | 7.24 | 5.2 | 0.6 | 0.3 | 19.6 |
| M14 × 2 | 14 | 13.73 | 24 | 23.67 | 27.71 | 26.75 | 9.09 | 8.51 | 6.2 | 0.6 | 0.3 | 22.5 |
| M16 × 2 | 16 | 15.73 | 27 | 26.67 | 31.18 | 30.14 | 10.32 | 9.68 | 7 | 0.8 | 0.4 | 25.3 |
| M20 × 2.5 | 20 | 19.67 | 34 | 33 | 39.26 | 37.29 | 12.88 | 12.12 | 8.8 | 0.8 | 0.4 | 31.4 |
| M24 × 3 | 24 | 23.67 | 41 | 40 | 47.34 | 45.2 | 15.44 | 14.56 | 10.5 | 0.8 | 0.4 | 38 |
| M30 × 3.5 | 30 | 29.67 | 50 | 49 | 57.74 | 55.37 | 19.48 | 17.92 | 13.1 | 0.8 | 0.4 | 46.6 |
| M36 × 4 | 36 | 35.61 | 60 | 58.8 | 69.28 | 66.44 | 23.38 | 21.72 | 15.8 | 0.8 | 0.4 | 55.9 |
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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 B18.2.3.3M, 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.
The grade symbol comes from Table 5 (clause 11.1), for example 32205 for S32205 or 174G for S17400 in H1150. With Supplementary Requirement S2 the marking goes on the heads of bolts of all sizes; if the area is too small, the grade symbol may go on one end and the manufacturer's identification on the other. Bolts under 1/4 in. [6 mm] are marked by agreement between purchaser and manufacturer.
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).
