Inch-Series Square Nuts with Wide Bearing Face for Anti-Rotation and Structural Timber Fastening Applications.
ASME B18.2.2 Square Nuts are inch-series internally threaded fasteners with a four-sided square profile that provides a wider bearing surface and natural anti-rotation behavior when seated against flat stock, timber, or square-punched holes, making them a preferred nut choice in structural timber connections, agricultural equipment, railroad hardware, anchor bolt assemblies, and specialty industrial fastening where the square geometry locks the nut against spinning during tightening without the need for a secondary wrench or tool. The ASME B18.2.2 standard governs all critical dimensional requirements for square nuts including width across flats, width across corners, nut thickness, chamfer, and thread specifications for nominal sizes ranging from 1/4 inch to 1 1/2 inches, ensuring consistent dimensional interchangeability across all compliant manufacturers within the American National Standard framework. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, these square nuts provide the corrosion resistance and long service life required in outdoor structural assemblies, coastal timber construction, marine dock hardware, agricultural facility framing, and chemical plant structural connections where standard carbon steel nuts would rust aggressively and eventually seize or fail. ASME B18.2.2 square nuts in ASTM A1082 stainless steel are fully compatible with ASME B18.2.1 hex bolts and square bolts in matching stainless steel material, providing complete corrosion-resistant bolted assemblies for the most demanding outdoor and industrial service environments. Full EN 10204 Type 3.1 material certification is available for all ASTM A1082 square nut lots for quality-controlled project supply.
| Nominal Size (in) | Basic Major Diameter | Width Across Flats, F | Width Across Corners, G | Thickness | Runout to Thread Axis, FIM | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Basic | Min. | Max. | Min. | Max. | Basic | Min. | Max. | |||
| 1/4 | 6.350 | 11.11 | 10.80 | 11.13 | 14.07 | 15.72 | 5.56 | 5.16 | 5.97 | 0.28 |
| 5/16 | 7.938 | 14.29 | 13.89 | 14.27 | 18.31 | 20.19 | 6.75 | 6.32 | 7.19 | 0.38 |
| 3/8 | 9.525 | 15.88 | 15.39 | 15.88 | 20.37 | 22.45 | 8.33 | 7.87 | 8.79 | 0.41 |
| 7/16 | 11.113 | 19.05 | 18.49 | 19.05 | 24.64 | 26.95 | 9.53 | 9.04 | 10.01 | 0.48 |
| 1/2 | 12.700 | 20.64 | 20.02 | 20.62 | 26.72 | 29.18 | 11.11 | 10.62 | 11.63 | 0.56 |
| 5/8 | 15.875 | 25.40 | 24.61 | 25.40 | 33.02 | 35.92 | 13.89 | 13.34 | 14.45 | 0.66 |
| 3/4 | 19.050 | 28.58 | 27.64 | 28.58 | 37.19 | 40.41 | 16.67 | 16.05 | 17.27 | 0.74 |
| 7/8 | 22.225 | 33.34 | 32.23 | 33.32 | 43.48 | 47.14 | 19.45 | 18.80 | 20.12 | 0.86 |
| 1 | 25.400 | 38.10 | 36.83 | 38.10 | 49.81 | 53.87 | 22.23 | 21.51 | 22.94 | 0.99 |
| 1 1/8 | 28.575 | 42.86 | 41.43 | 42.88 | 56.11 | 60.60 | 25.40 | 24.64 | 26.16 | 0.74 |
| 1 1/4 | 31.750 | 47.63 | 46.02 | 47.63 | 62.43 | 67.36 | 27.78 | 26.97 | 28.60 | 0.81 |
| 1 3/8 | 34.925 | 52.39 | 50.65 | 52.37 | 68.78 | 74.09 | 30.56 | 29.69 | 31.42 | 0.89 |
| 1 1/2 | 38.100 | 57.15 | 55.25 | 57.15 | 75.08 | 80.82 | 33.34 | 32.41 | 34.24 | 0.99 |
| Nominal Size | Basic Major Diameter of Thread | Width Across Flats, F | Width Across Corners, G | Thickness | Bearing Surface Runout to Thread Axis, FIM | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Basic | Min. | Max. | Min. | Max. | Basic | Min. | Max. | |||
| 1/4 | 0.2500 | 7/16 | 0.425 | 0.438 | 0.554 | 0.619 | 7/32 | 0.203 | 0.235 | 0.011 |
| 5/16 | 0.3125 | 9/16 | 0.547 | 0.562 | 0.721 | 0.795 | 17/64 | 0.249 | 0.283 | 0.015 |
| 3/8 | 0.3750 | 5/8 | 0.606 | 0.625 | 0.802 | 0.884 | 21/64 | 0.310 | 0.346 | 0.016 |
| 7/16 | 0.4375 | 3/4 | 0.728 | 0.750 | 0.970 | 1.061 | 3/8 | 0.356 | 0.394 | 0.019 |
| 1/2 | 0.5000 | 13/16 | 0.788 | 0.812 | 1.052 | 1.149 | 7/16 | 0.418 | 0.458 | 0.022 |
| 5/8 | 0.6250 | 1 | 0.969 | 1.000 | 1.300 | 1.414 | 35/64 | 0.525 | 0.569 | 0.026 |
| 3/4 | 0.7500 | 1 1/8 | 1.088 | 1.125 | 1.464 | 1.591 | 21/32 | 0.632 | 0.680 | 0.029 |
| 7/8 | 0.8750 | 1 5/16 | 1.269 | 1.312 | 1.712 | 1.856 | 49/64 | 0.740 | 0.792 | 0.034 |
| 1 | 1.0000 | 1 1/2 | 1.450 | 1.500 | 1.961 | 2.121 | 7/8 | 0.847 | 0.903 | 0.039 |
| 1 1/8 | 1.1250 | 1 11/16 | 1.631 | 1.688 | 2.209 | 2.386 | 1 | 0.970 | 1.030 | 0.029 |
| 1 1/4 | 1.2500 | 1 7/8 | 1.812 | 1.875 | 2.458 | 2.652 | 1 3/32 | 1.062 | 1.126 | 0.032 |
| 1 3/8 | 1.3750 | 2 1/16 | 1.994 | 2.062 | 2.708 | 2.917 | 1 13/64 | 1.169 | 1.237 | 0.035 |
| 1 1/2 | 1.5000 | 2 1/4 | 2.175 | 2.250 | 2.956 | 3.182 | 1 5/16 | 1.276 | 1.348 | 0.039 |
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).
