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 – Dimensions, Specifications & Standards
Flat Countersunk Head Cap Screws for Flush-Mount Assemblies.
ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws are inch-series fasteners with a flat, conical head designed to sit flush with or below the surface of a countersunk hole — ideal for aerospace panels, machinery guards, tooling plates, and precision instruments. B18.3 governs head diameter, head angle (typically 82°), head height, hexagonal socket size, body diameter, thread length, and key engagement depth. When used under ASTM A1014/A1014M for UNS N07718 alloy bolting, these screws deliver excellent corrosion resistance and high tensile strength for marine, chemical processing, and high-temperature service. ASTM A574 alloy steel grades provide 180,000 PSI minimum tensile strength. Proper countersink angle and depth preparation is critical for full bearing contact and flush seating.
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 |
Satisfaction Survey
