High-Strength Inch-Series Allen Drive Cap Screws for Confined-Space and Precision Mechanical Bolting.
ASME B18.3 Hexagon Socket Head Cap Screws are inch-series precision fasteners featuring a cylindrical head with an internal hexagonal Allen drive socket, engineered to develop high clamping forces in applications where external wrench access is restricted by surrounding components, making them the standard fastener choice in precision machine tools, hydraulic manifolds, dies and molds, aerospace structures, robotics, and automated assembly equipment where compact fastening with maximum strength in minimum space is a design imperative. The ASME B18.3 standard establishes dimensional requirements for head diameter, head height, hexagonal socket size, key engagement depth, body diameter, thread length, and all associated tolerances, ensuring precise dimensional interchangeability and consistent performance across all compliant manufacturers. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, these socket head cap screws deliver high tensile strength, excellent fatigue resistance, and outstanding corrosion resistance in aggressive service environments including chemical process equipment, marine hardware, food and pharmaceutical machinery, and high-humidity industrial settings where standard alloy steel socket screws would suffer from surface rust and corrosion-induced galling. The internal socket drive allows tightening with a hex key in applications where open-end or box wrenches physically cannot be used, providing exceptional versatility in compact mechanical assembly designs. Every ASTM A1082 socket head cap screw lot is backed by full EN 10204 Type 3.1 material certification for quality-assured procurement.
| Nominal Size | Basic Screw Diameter (in.) | Body Diameter, D (mm) | Head Diameter, A (mm) | Head Height, H (mm) | Maximum Chamfer or Radius, C (mm) | Nominal Hexagon Socket Size, J | Socket Width Across Flats, J (mm) | Minimum Key Engagement, T (mm) | Minimum Wall Thickness, G (mm) | Maximum Chamfer or Radius, K (mm) | Fillet Juncture Diameter, F (mm) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Max. | Min. | Max. | Min. | Nom. | Dec. (mm) | Max. | Min. | Max. | Min. | ||||||
| #0 | 0.0600 | 1.524 | 1.443 | 2.438 | 2.311 | 1.524 | 1.448 | 0.102 | ... | 1.27 | 1.295 | 1.27 | 0.635 | 0.508 | 0.178 | 1.88 | 1.575 |
| #1 | 0.0730 | 1.854 | 1.765 | 2.997 | 2.845 | 1.854 | 1.778 | 0.127 | 1/16 | 1.575 | 1.613 | 1.588 | 0.787 | 0.635 | 0.178 | 2.21 | 1.905 |
| #2 | 0.0860 | 2.184 | 2.088 | 3.556 | 3.404 | 2.184 | 2.108 | 0.203 | 5/64 | 1.981 | 2.009 | 1.984 | 0.965 | 0.737 | 0.178 | 2.591 | 2.286 |
| #3 | 0.0990 | 2.515 | 2.41 | 4.089 | 3.912 | 2.515 | 2.413 | 0.203 | 5/64 | 1.981 | 2.009 | 1.984 | 1.118 | 0.864 | 0.178 | 2.921 | 2.591 |
| #4 | 0.1120 | 2.845 | 2.731 | 4.648 | 4.47 | 2.845 | 2.743 | 0.229 | 3/32 | 2.388 | 2.418 | 2.38 | 1.295 | 0.965 | 0.203 | 3.302 | 2.972 |
| #5 | 0.1250 | 3.175 | 3.053 | 5.207 | 5.029 | 3.175 | 3.073 | 0.305 | 3/32 | 2.388 | 2.418 | 2.38 | 1.448 | 1.092 | 0.203 | 3.683 | 3.353 |
| #6 | 0.1380 | 3.505 | 3.376 | 5.74 | 5.486 | 3.505 | 3.404 | 0.33 | 7/64 | 2.769 | 2.822 | 2.779 | 1.626 | 1.194 | 0.203 | 4.013 | 3.658 |
| #8 | 0.1640 | 4.166 | 4.026 | 6.858 | 6.528 | 4.166 | 4.039 | 0.356 | 9/64 | 3.581 | 3.622 | 3.571 | 1.956 | 1.422 | 0.203 | 4.775 | 4.369 |
| #10 | 0.1900 | 4.826 | 4.674 | 7.925 | 7.569 | 4.826 | 4.699 | 0.457 | 5/32 | 3.962 | 4.031 | 3.967 | 2.286 | 1.651 | 0.203 | 5.537 | 5.131 |
| #12 | 0.2160 | 5.486 | 5.321 | 8.23 | 7.976 | 5.486 | 5.334 | 0.559 | 5/32 | 3.962 | 4.031 | 3.967 | 2.616 | 2.083 | 0.254 | - | - |
| 1/4 | 0.2500 | 6.35 | 6.185 | 9.525 | 8.992 | 6.35 | 6.198 | 0.635 | 3/16 | 4.775 | 4.826 | 4.763 | 3.048 | 2.413 | 0.254 | 7.061 | 6.63 |
| 5/16 | 0.3125 | 7.938 | 7.755 | 11.913 | 11.328 | 7.925 | 7.772 | 0.838 | 1/4 | 6.35 | 6.426 | 6.35 | 3.835 | 3.023 | 0.254 | 8.814 | 8.357 |
| 3/8 | 0.3750 | 9.525 | 9.342 | 14.275 | 13.716 | 9.525 | 9.347 | 1.016 | 5/16 | 7.925 | 8.026 | 7.938 | 4.623 | 3.632 | 0.254 | 10.541 | 10.084 |
| 7/16 | 0.4375 | 11.113 | 10.907 | 16.662 | 16.027 | 11.125 | 10.922 | 1.194 | 3/8 | 9.525 | 9.627 | 9.525 | 5.41 | 4.216 | 0.381 | 12.294 | 11.811 |
| 1/2 | 0.5000 | 12.7 | 12.494 | 19.05 | 18.415 | 12.7 | 12.497 | 1.397 | 3/8 | 9.525 | 9.627 | 9.525 | 6.223 | 4.826 | 0.381 | 14.021 | 13.487 |
| 9/16 | 0.5625 | 14.288 | 14.067 | 21.412 | 21.006 | 14.275 | 14.072 | 1.575 | 7/16 | 11.1 | 11.227 | 11.113 | 7.01 | 5.436 | 0.381 | - | - |
| 5/8 | 0.6250 | 15.875 | 15.654 | 23.825 | 23.216 | 15.875 | 15.647 | 1.778 | 1/2 | 12.7 | 12.827 | 12.7 | 7.798 | 6.045 | 0.381 | 17.501 | 16.866 |
| 3/4 | 0.7500 | 19.05 | 18.811 | 28.575 | 27.788 | 19.05 | 18.796 | 2.159 | 5/8 | 15.875 | 16.027 | 15.875 | 9.398 | 7.239 | 0.381 | 21.031 | 20.32 |
| 7/8 | 0.8750 | 22.225 | 21.963 | 33.325 | 32.791 | 22.225 | 21.946 | 2.54 | 3/4 | 19.05 | 19.228 | 19.05 | 10.973 | 8.458 | 0.508 | 24.46 | 23.673 |
| 1 | 1.0000 | 25.4 | 25.11 | 38.1 | 37.49 | 25.4 | 25.095 | 2.896 | 3/4 | 19.05 | 19.228 | 19.05 | 12.573 | 9.652 | 0.508 | 27.94 | 27.127 |
| 1 1/8 | 1.1250 | 28.575 | 28.158 | 42.875 | 42.291 | 28.575 | 28.219 | 3.277 | 7/8 | 22.225 | 22.479 | 22.225 | 14.148 | 10.871 | 0.508 | 31.369 | 30.429 |
| 1 1/4 | 1.2500 | 31.75 | 31.333 | 47.625 | 47.041 | 31.75 | 31.394 | 3.658 | 7/8 | 22.225 | 22.479 | 22.225 | 15.748 | 12.065 | 0.508 | 34.798 | 33.858 |
| 1 3/8 | 1.3750 | 34.925 | 34.463 | 52.375 | 51.765 | 34.925 | 34.544 | 4.064 | 1 | 25.4 | 25.908 | 25.4 | 17.323 | 13.284 | 0.508 | 38.227 | 37.236 |
| 1 1/2 | 1.5000 | 38.1 | 37.638 | 57.15 | 56.49 | 38.1 | 37.719 | 4.47 | 1 | 25.4 | 25.908 | 25.4 | 18.923 | 14.478 | 0.508 | 41.656 | 40.665 |
| 1 3/4 | 1.7500 | 44.45 | 43.929 | 66.675 | 65.964 | 44.45 | 44.044 | 5.258 | 1 1/4 | 31.75 | 32.385 | 31.75 | 22.098 | 16.891 | 0.508 | 48.514 | 47.473 |
| 2 | 2.0000 | 50.8 | 50.241 | 76.2 | 75.438 | 50.8 | 50.368 | 6.045 | 1 1/2 | 38.1 | 38.862 | 38.1 | 25.273 | 19.304 | 0.508 | 55.372 | 54.051 |
| 2 1/4 | 2.2500 | 57.15 | 56.591 | 85.725 | 84.938 | 57.15 | 56.693 | 6.833 | 1 3/4 | 44.45 | 45.339 | 44.45 | 28.448 | 21.717 | 0.914 | 62.23 | 60.909 |
| 2 1/2 | 2.5000 | 63.5 | 62.896 | 95.25 | 94.412 | 63.5 | 63.017 | 7.62 | 1 3/4 | 44.45 | 45.339 | 44.45 | 31.623 | 24.13 | 0.914 | 69.088 | 67.615 |
| 2 3/4 | 2.7500 | 69.85 | 69.246 | 104.775 | 103.886 | 69.85 | 69.342 | 8.433 | 2 | 50.8 | 51.816 | 50.8 | 34.798 | 26.543 | 0.914 | 75.946 | 74.574 |
| 3 | 3.0000 | 76.2 | 75.596 | 114.3 | 113.386 | 76.2 | 75.667 | 9.195 | 2 1/4 | 57.15 | 58.293 | 57.15 | 37.973 | 28.956 | 0.914 | 82.804 | 81.432 |
| 3 1/4 | 3.2500 | 82.55 | 81.946 | 123.825 | 122.86 | 82.55 | 81.991 | 10.008 | 2 1/4 | 57.15 | 58.293 | 57.15 | 41.148 | 31.369 | 0.914 | 89.662 | 88.29 |
| 3 1/2 | 3.5000 | 88.9 | 88.296 | 133.35 | 132.359 | 88.9 | 88.341 | 10.82 | 2 3/4 | 69.85 | 71.247 | 69.85 | 44.323 | 33.782 | 0.914 | 96.52 | 95.148 |
| 3 3/4 | 3.7500 | 95.25 | 94.646 | 142.875 | 141.834 | 95.25 | 94.666 | 11.633 | 2 3/4 | 69.85 | 71.247 | 69.85 | 47.498 | 36.195 | 0.914 | 103.378 | 102.006 |
| 4 | 4.0000 | 101.6 | 100.996 | 152.4 | 151.333 | 101.6 | 100.99 | 12.421 | 3 | 76.2 | 77.724 | 76.2 | 50.673 | 38.608 | 0.914 | 110.236 | 108.864 |
| Nominal Length | Nominal Size, Tolerances on Lengths (mm) | |||
|---|---|---|---|---|
| 0 Through 9.525, Incl. |
11.112 Through 19.05, Incl. |
22.225 Through 38.1, Incl. |
Over 38.1 | |
| Up to 25.4, incl. | -0.762 | -0.762 | -1.27 | ... |
| Over 25.4 to 63.5, incl. | -1.016 | -1.524 | -2.54 | -4.572 |
| Over 63.5 to 152.4, incl. | -1.524 | -2.032 | -3.556 | -5.08 |
| Over 152.4 | -3.048 | -3.048 | -5.08 | -6.096 |
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 B18.3, 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).
