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 B18.2.1 Heavy Hex Bolts
Structural bolts with enlarged heads designed for high-strength steel connections in bridges, buildings, and heavy industrial frameworks.
ASME B18.2.1 Heavy Hex Bolts are engineered with a larger head size (width-across-flats) and greater bearing surface than standard hex bolts, specifically to meet the rigorous demands of structural steel connections. The enlarged head distributes the immense clamping forces generated during tensioning over a wider area, preventing deformation of the connected steel plates and ensuring joint integrity. These bolts are the backbone of modern infrastructure, used extensively in the erection of steel frames for high-rise buildings, bridges, and transmission towers. They are often specified in conjunction with high-strength materials such as ASTM A325 or A490 and are installed using calibrated wrenches or turn-of-nut methods to achieve precise preload. The dimensional consistency mandated by ASME B18.2.1 ensures that these bolts mate correctly with heavy hex nuts and hardened washers, forming a complete and reliable structural fastening system.
ASME B18.2.1 Heavy Hex Bolts Dimensions (mm)
| Nominal Size or Basic Product Diameter | Full-Size Body Diameter, E | Width Across Flats, F | Width Across Corners, G | Head Height, H | Radius of Fillet, R | Nominal Thread Length, LT | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Basic | Max. | Min. | Max. | Min. | Basic | Max. | Min. | Max. | Min. | 152.4mm and Shorter | Over 152.4mm | ||
| 3/8 | 9.525 | 9.855 | 9.144 | 17.463 | 17.475 | 16.993 | 20.168 | 19.380 | 6.350 | 6.807 | 5.740 | 0.762 | 0.254 | 25.400 | 31.750 |
| 1/2 | 12.700 | 13.081 | 12.243 | 22.225 | 22.225 | 21.590 | 25.654 | 24.613 | 8.731 | 9.246 | 7.671 | 0.762 | 0.254 | 31.750 | 38.100 |
| 5/8 | 15.875 | 16.307 | 15.367 | 26.988 | 26.975 | 26.187 | 31.166 | 29.845 | 10.716 | 11.278 | 9.601 | 1.524 | 0.508 | 38.100 | 44.450 |
| 3/4 | 19.050 | 19.507 | 18.517 | 31.750 | 31.750 | 30.785 | 36.652 | 35.128 | 12.700 | 13.310 | 11.557 | 1.524 | 0.508 | 44.450 | 50.800 |
| 7/8 | 22.225 | 22.733 | 21.641 | 36.513 | 36.525 | 35.408 | 42.164 | 40.361 | 14.684 | 15.342 | 13.487 | 1.524 | 0.508 | 50.800 | 57.150 |
| 1 | 25.400 | 25.959 | 24.790 | 41.275 | 41.275 | 40.005 | 47.650 | 45.618 | 17.066 | 17.780 | 15.011 | 2.286 | 0.762 | 57.150 | 63.500 |
| 1 1/8 | 28.575 | 29.185 | 27.889 | 46.038 | 46.025 | 44.602 | 53.162 | 50.851 | 19.050 | 19.812 | 16.713 | 2.286 | 0.762 | 63.500 | 69.850 |
| 1 1/4 | 31.750 | 32.436 | 31.064 | 50.800 | 50.800 | 49.225 | 58.649 | 56.109 | 21.431 | 22.250 | 19.025 | 2.286 | 0.762 | 69.850 | 76.200 |
| 1 3/8 | 34.925 | 35.662 | 34.163 | 55.563 | 55.575 | 53.823 | 64.160 | 61.366 | 23.019 | 23.876 | 20.574 | 2.286 | 0.762 | 76.200 | 82.550 |
| 1 1/2 | 38.100 | 38.887 | 37.338 | 60.325 | 60.325 | 58.420 | 69.647 | 66.599 | 25.400 | 26.314 | 22.911 | 2.286 | 0.762 | 82.550 | 88.900 |
| 1 5/8 | 41.275 | 42.113 | 40.411 | 65.088 | 65.075 | 63.017 | 75.159 | 71.857 | 27.781 | 28.346 | 24.841 | 2.286 | 0.762 | 88.900 | 95.250 |
| 1 3/4 | 44.450 | 45.339 | 43.586 | 69.850 | 69.850 | 67.615 | 80.645 | 77.089 | 29.369 | 30.378 | 26.772 | 3.048 | 1.016 | 95.250 | 101.600 |
| 1 7/8 | 47.625 | 48.565 | 46.711 | 74.613 | 74.625 | 72.238 | 86.157 | 82.347 | 31.750 | 32.410 | 28.702 | 3.048 | 1.016 | 101.600 | 107.950 |
| 2 | 50.800 | 51.791 | 49.886 | 79.375 | 79.375 | 76.835 | 91.643 | 87.605 | 34.131 | 35.255 | 29.845 | 3.048 | 1.016 | 107.950 | 114.300 |
| 2 1/4 | 57.150 | 58.547 | 56.236 | 88.900 | 88.900 | 86.055 | 102.641 | 98.095 | 38.100 | 39.319 | 33.706 | 4.826 | 1.524 | 120.650 | 127.000 |
| 2 1/2 | 63.500 | 64.999 | 62.509 | 98.425 | 98.425 | 95.250 | 113.640 | 108.585 | 42.069 | 43.383 | 37.567 | 4.826 | 1.524 | 133.350 | 139.700 |
| 2 3/4 | 69.850 | 71.806 | 68.859 | 107.950 | 107.950 | 104.445 | 124.638 | 119.075 | 46.038 | 47.473 | 41.453 | 4.826 | 1.524 | 146.050 | 152.400 |
| 3 | 76.200 | 78.257 | 75.209 | 117.475 | 117.475 | 113.665 | 135.636 | 129.591 | 50.800 | 52.324 | 46.101 | 4.826 | 1.524 | 158.750 | 165.100 |
ASME B18.2.1 Heavy Hex Bolts Length Tolerance (mm)
| Nominal Length | Nominal Size (inches) | |||||
|---|---|---|---|---|---|---|
| 1/4 to 3/8 | 7/16 and 1/2 | 9/16 to 3/4 | 7/8 and 1 | 1 1/8 to 1 1/2 | Over 1 1/2 | |
| Up to 25.4 mm, incl. | +0.508 0.762 |
+0.508 0.762 |
+0.508 0.762 |
... | ... | ... |
| Over 25.4 mm to 63.5 mm, incl. | +0.508 1.016 |
+1.016 1.524 |
+1.524 2.032 |
+2.032 2.54 |
+3.048 3.048 |
+4.572 4.572 |
| Over 63.5 mm to 101.6 mm, incl. | +1.016 1.524 |
+1.524 2.032 |
+2.032 2.54 |
+2.54 3.556 |
+4.064 4.064 |
+5.08 5.08 |
| Over 101.6 mm to 152.4 mm, incl. | +1.524 2.54 |
+2.032 2.54 |
+2.54 2.54 |
+3.048 4.064 |
+4.572 4.572 |
+5.588 5.588 |
| Longer than 152.4 mm | +2.54 4.572 |
+3.048 4.572 |
+3.556 4.572 |
+4.064 5.08 |
+5.588 5.588 |
+6.096 6.096 |
ASME B18.2.1 Heavy Hex Bolts Dimensions (Inch)
| Nominal Size or Basic Product Diameter | Full-Size Body Diameter, E | Width Across Flats, F | Width Across Corners, G | Head Height, H | Radius of Fillet, R | Nominal Thread Length for Bolt Lengths, LT | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Basic | Max. | Min. | Max. | Min. | Basic | Max. | Min. | Max. | Min. | 6 in. and Shorter | Over 6 in. | ||
| 3/8 | 0.3750 | 0.388 | 0.360 | 11/16 | 0.688 | 0.669 | 0.794 | 0.763 | 1/4 | 0.268 | 0.226 | 0.03 | 0.01 | 1.000 | 1.250 |
| 1/2 | 0.5000 | 0.515 | 0.482 | 7/8 | 0.875 | 0.850 | 1.010 | 0.969 | 11/32 | 0.364 | 0.302 | 0.03 | 0.01 | 1.250 | 1.500 |
| 5/8 | 0.6250 | 0.642 | 0.605 | 1 1/16 | 1.062 | 1.031 | 1.227 | 1.175 | 27/64 | 0.444 | 0.378 | 0.06 | 0.02 | 1.500 | 1.750 |
| 3/4 | 0.7500 | 0.768 | 0.729 | 1 1/4 | 1.250 | 1.212 | 1.443 | 1.383 | 1/2 | 0.524 | 0.455 | 0.06 | 0.02 | 1.750 | 2.000 |
| 7/8 | 0.8750 | 0.895 | 0.852 | 1 7/16 | 1.438 | 1.394 | 1.660 | 1.589 | 37/64 | 0.604 | 0.531 | 0.06 | 0.02 | 2.000 | 2.250 |
| 1 | 1.0000 | 1.022 | 0.976 | 1 5/8 | 1.625 | 1.575 | 1.876 | 1.796 | 43/64 | 0.700 | 0.591 | 0.09 | 0.03 | 2.250 | 2.500 |
| 1 1/8 | 1.1250 | 1.149 | 1.098 | 1 13/16 | 1.812 | 1.756 | 2.093 | 2.002 | 3/4 | 0.780 | 0.658 | 0.09 | 0.03 | 2.500 | 2.750 |
| 1 1/4 | 1.2500 | 1.277 | 1.223 | 2 | 2.000 | 1.938 | 2.309 | 2.209 | 27/32 | 0.876 | 0.749 | 0.09 | 0.03 | 2.750 | 3.000 |
| 1 3/8 | 1.3750 | 1.404 | 1.345 | 2 3/16 | 2.188 | 2.119 | 2.526 | 2.416 | 29/32 | 0.940 | 0.810 | 0.09 | 0.03 | 3.000 | 3.250 |
| 1 1/2 | 1.5000 | 1.531 | 1.470 | 2 3/8 | 2.375 | 2.300 | 2.742 | 2.622 | 1 | 1.036 | 0.902 | 0.09 | 0.03 | 3.250 | 3.500 |
| 1 5/8 | 1.6250 | 1.658 | 1.591 | 2 9/16 | 2.562 | 2.481 | 2.959 | 2.829 | 1 3/32 | 1.116 | 0.978 | 0.09 | 0.03 | 3.500 | 3.750 |
| 1 3/4 | 1.7500 | 1.785 | 1.716 | 2 3/4 | 2.750 | 2.662 | 3.175 | 3.035 | 1 5/32 | 1.196 | 1.054 | 0.12 | 0.04 | 3.750 | 4.000 |
| 1 7/8 | 1.8750 | 1.912 | 1.839 | 2 15/16 | 2.938 | 2.844 | 3.392 | 3.242 | 1 1/4 | 1.276 | 1.130 | 0.12 | 0.04 | 4.000 | 4.250 |
| 2 | 2.0000 | 2.039 | 1.964 | 3 1/8 | 3.125 | 3.025 | 3.608 | 3.449 | 1 11/32 | 1.388 | 1.175 | 0.12 | 0.04 | 4.250 | 4.500 |
| 2 1/4 | 2.2500 | 2.305 | 2.214 | 3 1/2 | 3.500 | 3.388 | 4.041 | 3.862 | 1 1/2 | 1.548 | 1.327 | 0.19 | 0.06 | 4.750 | 5.000 |
| 2 1/2 | 2.5000 | 2.559 | 2.461 | 3 7/8 | 3.875 | 3.750 | 4.474 | 4.275 | 1 21/32 | 1.708 | 1.479 | 0.19 | 0.06 | 5.250 | 5.500 |
| 2 3/4 | 2.7500 | 2.827 | 2.711 | 4 1/4 | 4.250 | 4.112 | 4.907 | 4.688 | 1 13/16 | 1.869 | 1.632 | 0.19 | 0.06 | 5.750 | 6.000 |
| 3 | 3.0000 | 3.081 | 2.961 | 4 5/8 | 4.625 | 4.475 | 5.340 | 5.102 | 2 | 2.060 | 1.815 | 0.19 | 0.06 | 6.250 | 6.500 |
ASME B18.2.1 Heavy Hex Bolts Length Length Tolerance (Inch)
| Nominal Length | Nominal Size | |||||
|---|---|---|---|---|---|---|
| 1/4 to 3/8 | 7/16 and 1/2 | 9/16 to 3/4 | 7/8 and 1 | 1 1/8 to 1 1/2 | Over 1 1/2 | |
| Up to 1 in., incl. | +0.02 0.03 |
+0.02 0.03 |
+0.02 0.03 |
... | ... | ... |
| Over 1 in. to 2 1/2 in., incl. | +0.02 0.04 |
+0.04 0.06 |
+0.06 0.08 |
+0.08 0.10 |
+0.12 0.12 |
+0.18 0.18 |
| Over 2 1/2 in. to 4 in., incl. | +0.04 0.06 |
+0.06 0.08 |
+0.08 0.10 |
+0.10 0.14 |
+0.16 0.16 |
+0.20 0.20 |
| Over 4 in. to 6 in., incl. | +0.06 0.10 |
+0.08 0.10 |
+0.10 0.10 |
+0.12 0.16 |
+0.18 0.18 |
+0.22 0.22 |
| Longer than 6 in. | +0.10 0.18 |
+0.12 0.18 |
+0.14 0.18 |
+0.16 0.20 |
+0.22 0.22 |
+0.24 0.24 |
Frequently Asked Questions
- What does ASME B18.2.1 heavy hex bolts cover?
- ASME B18.2.1 is the inch dimensional standard for heavy hex bolts. It defines head dimensions, body diameter, thread length, total length, drive recess, and tolerances so any compliant heavy hex bolts interchanges with standard nuts, washers and wrenches across manufacturers.
- What size range is available for heavy hex bolts under ASME B18.2.1?
- heavy hex bolts under ASME B18.2.1 covers 1/2 in to 3 in nominal diameter for high-strength bolting. TorqBolt manufactures the full range in ASTM A193 Grades B7, B7M, B8, B8M and the full ASTM A320 cryogenic counterpart on customer specification.
- What is the metric/inch counterpart of ASME B18.2.1 heavy hex bolts?
- The companion specification for heavy hex bolts is ASME B18.2.3.6 metric heavy hex. Both standards share equivalent functional dimensions but use the corresponding measurement system (inch vs metric ISO M-series).
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