Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws Dimension Standard
Flush-Mount Inch-Series Socket Screws for Smooth, Unobstructed Surfaces in Aerospace, Marine, and Precision Assemblies.
ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws are inch-series precision fasteners featuring a flat conical head at an 82° included angle designed to sit flush with or below the mating surface when installed in a properly prepared countersunk hole — making them ideal for aerospace panels, precision tooling plates, machinery guards, optical instruments, and consumer product assemblies where protruding fastener heads are functionally or aesthetically unacceptable. The ASME B18.3 standard precisely defines dimensional requirements including head diameter, head height, socket size, hexagon key engagement depth, body diameter, thread length, and all associated tolerances, ensuring precision fit between screw and countersink across all compliant manufacturing sources. When manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, these socket flat countersunk cap screws offer high tensile strength, excellent corrosion resistance, and clean aesthetic appearance required in marine equipment, food processing machinery, medical device structures, and architectural metal assemblies. Proper countersink preparation at the correct 82° angle and depth in the mating component is critical to achieving full bearing contact between the conical head and countersunk surface, ensuring load is transferred efficiently and the head seats fully flush. All ASTM A1082 flat countersunk socket cap screws are supplied with full material test documentation for quality-critical applications.
ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws Dimension (mm)
| Nominal Size | Body Diameter, D | Head Diameter, A | Reference Head Height, H | Protrusion Gage Diameter, G | Protrusion, P | Nominal Hexagon Socket Size, J | Minimum Key Engagement, T | Maximum Fillet Transition Diameter, F | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. | Min. | Max. | ||||
| 0 (0.0600) | 1.524 | 1.442 | 3.505 | 2.971 | 1.117 | 1.981 | 1.955 | 1.117 | 0.660 | 0.902 | 0.889 | 0.635 | 1.828 |
| 1 (0.0730) | 1.854 | 1.765 | 4.267 | 3.632 | 1.371 | 2.565 | 2.540 | 1.219 | 0.711 | 1.295 | 1.270 | 0.787 | 2.260 |
| 2 (0.0860) | 2.184 | 2.087 | 5.003 | 4.267 | 1.625 | 3.149 | 3.124 | 1.295 | 0.787 | 1.295 | 1.270 | 0.965 | 2.692 |
| 3 (0.0990) | 2.514 | 2.410 | 5.740 | 4.902 | 1.854 | 3.759 | 3.733 | 1.371 | 0.838 | 1.613 | 1.588 | 1.117 | 3.022 |
| 4 (0.1120) | 2.844 | 2.730 | 6.477 | 5.537 | 2.108 | 4.368 | 4.343 | 1.447 | 0.914 | 1.613 | 1.588 | 1.397 | 3.454 |
| 5 (0.1250) | 3.175 | 3.053 | 7.137 | 6.096 | 2.286 | 4.978 | 4.953 | 1.498 | 0.939 | 2.009 | 1.984 | 1.549 | 3.886 |
| 6 (0.1380) | 3.505 | 3.375 | 7.797 | 6.680 | 2.463 | 5.588 | 5.562 | 1.524 | 0.939 | 2.009 | 1.984 | 1.676 | 4.267 |
| 8 (0.1640) | 4.165 | 4.025 | 9.118 | 7.899 | 2.844 | 6.781 | 6.756 | 1.600 | 0.990 | 2.418 | 2.38 | 1.930 | 4.927 |
| 10 (0.1900) | 4.826 | 4.673 | 10.439 | 9.118 | 3.225 | 7.950 | 7.924 | 1.676 | 1.041 | 3.226 | 3.175 | 2.209 | 5.588 |
| 12 (0.2158) | 5.481 | 5.339 | 11.430 | 10.414 | 3.429 | 9.144 | 9.118 | 1.752 | 1.066 | 3.226 | 3.175 | 2.387 | 6.248 |
| 1/4 (0.2500) | 6.350 | 6.184 | 13.487 | 12.192 | 4.089 | 10.769 | 10.744 | 1.828 | 1.092 | 4.031 | 3.967 | 2.819 | 7.112 |
| 5/16 (0.3125) | 7.937 | 7.747 | 16.662 | 15.240 | 5.029 | 13.690 | 13.665 | 1.981 | 1.193 | 4.826 | 4.763 | 3.429 | 8.712 |
| 3/8 (0.3750) | 9.525 | 9.342 | 19.837 | 18.288 | 5.943 | 16.586 | 16.560 | 2.235 | 1.270 | 5.631 | 5.555 | 4.038 | 10.287 |
| 7/16 (0.4375) | 11.112 | 10.906 | 21.437 | 19.837 | 5.943 | 17.526 | 17.475 | 2.641 | 1.600 | 6.426 | 6.35 | 4.038 | 11.887 |
| 1/2 (0.5000) | 12.700 | 12.494 | 23.825 | 22.148 | 6.375 | 18.770 | 18.745 | 3.327 | 2.209 | 8.026 | 7.938 | 4.368 | 13.462 |
| 5/8 (0.6250) | 15.875 | 15.654 | 30.175 | 28.244 | 8.229 | 24.434 | 24.409 | 3.708 | 2.438 | 9.627 | 9.525 | 5.588 | 16.637 |
| 3/4 (0.7500) | 19.050 | 18.811 | 36.525 | 34.417 | 10.058 | 30.124 | 30.099 | 4.318 | 2.667 | 12.827 | 12.7 | 5.588 | 19.812 |
| 7/8 (0.8750) | 22.225 | 21.963 | 42.875 | 40.741 | 11.887 | 35.839 | 35.814 | 4.191 | 2.997 | 14.427 | 14.288 | 6.299 | 22.987 |
| 1 (1.0000) | 25.400 | 25.110 | 49.225 | 46.761 | 13.716 | 41.529 | 41.503 | 4.597 | 3.302 | 16.027 | 15.875 | 7.543 | 26.162 |
| 1 1/8 (1.1250) | 28.575 | 28.158 | 55.575 | 52.806 | 15.519 | 47.218 | 47.193 | 4.978 | 3.556 | 19.228 | 19.05 | 8.255 | 30.149 |
| 1 1/4 (1.2500) | 31.750 | 31.333 | 61.925 | 58.826 | 17.348 | 52.908 | 52.882 | 5.384 | 3.810 | 22.479 | 22.225 | 9.093 | 33.324 |
| 1 3/8 (1.3750) | 34.925 | 34.462 | 68.275 | 64.846 | 19.177 | 58.572 | 58.547 | 5.791 | 4.114 | 22.479 | 22.225 | 10.210 | 36.499 |
| 1 1/2 (1.5000) | 38.100 | 37.637 | 74.625 | 70.891 | 21.005 | 64.262 | 64.236 | 6.172 | 4.394 | 25.908 | 25.4 | 11.049 | 39.674 |
ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws Length Tolerances(mm)
| Nominal Length | Nominal Size, Tolerances on Lengths | ||
|---|---|---|---|
| 0 Through 3/8, Incl. |
7/16 Through 3/4, Incl. |
7/8 Through 1 1/2, Incl. |
|
| Up to 25.4, incl. | -0.762 | -0.762 | -1.270 |
| Over 25.4 to 63.5, incl. | -1.016 | -1.524 | -2.540 |
| Over 63.5 to 152.4, incl. | -1.524 | -2.032 | -3.556 |
| Over 152.4 | -3.048 | -3.048 | -5.080 |
Frequently Asked Questions
What stainless steel grades does ASTM A1082 cover for din 7991?
ASTM A1082 covers duplex grades (S31803/2205, S32205/2205, S32750/2507, S32760/Zeron 100, S39277/AL-6XN) and precipitation-hardening grades (S17400/17-4 PH, S17700/17-7 PH, S15700/15-7 PH, S35500/AM-355) - all available for this product family at TorqBolt.
What is the standard dimensional reference for these din 7991?
This product follows ASME B18.3, the dimensional standard for din 7991 in stainless steel. Material chemistry, mechanical properties and heat treatment follow ASTM A1082/A1082M. TorqBolt supplies both inch-series and metric sizes per the applicable ASME or ISO drawing.
Are A1082 din 7991 suitable for sour service (NACE MR0175)?
Yes, with hardness control. NACE MR0175 / ISO 15156 permits duplex grades S31803, S32205, S32750, S32760 at 28 HRC max for sour service. 17-4 PH (S17400) at H1150 condition (28 HRC) is the most common PH grade qualified for sour service. TorqBolt provides NACE-MR0175 compliant heat-treat reports.
What is the typical strength of A1082 super-duplex 2507 (S32750) din 7991?
Super-duplex 2507 (S32750) per A1082: tensile 116 ksi (800 MPa) min, yield 80 ksi (550 MPa) min, elongation 15% min, 32 HRC max. PREN ≈ 42 - suitable for seawater, brine and chloride-rich pressure-vessel service. Higher strength than austenitic A193 B8M while offering pitting resistance well above 304/316.
References & Standards
- ASTM A1082 / A1082M - Standard Specification for High-Strength Precipitation-Hardening and Duplex Stainless Steel Bolting for Special-Purpose Applications (current edition 2016, active)
- ASTM A962 / A962M - General Requirements for Special-Purpose Bolting Materials
- ASTM A370 - Mechanical Testing of Steel Products
- NACE MR0175 / ISO 15156 - Sour-service hardness limits for petroleum & natural gas industries
- ASME B18 series - Dimensional standards for bolts, screws, nuts, studs
- ISO 4032 / 4033 / 4035 - Metric hexagon nut dimensional standards
Satisfaction Survey
