ASME B 18.2.1 Hex Bolts (2012); is the governing dimensional standard for inch-series hex bolts used in industrial, mechanical, and structural applications throughout North America and worldwide markets that use imperial measurements.
Dimensions of ASME B18.2.1 Hex Bolts
| Thread Size (d) | 1/4 | 5/16 | 3/8 | 7/16 | 1/2 | 5/8 | 3/4 | 7/8 | 1 | 1-1/8 | 1-1/4 | 1-3/8 | 1-1/2 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PP | UNC | 20 | 18 | 16 | 14 | 13 | 11 | 10 | 9 | 8 | 7 | 7 | 6 | 6 |
| UNF | 28 | 24 | 24 | 20 | 20 | 18 | 16 | 14 | 12 | 12 | 12 | 12 | 12 | |
| 8-UN | – | – | – | – | – | – | – | – | – | 8 | 8 | 8 | 8 | |
| ds | max | 0.26 | 0.324 | 0.388 | 0.452 | 0.515 | 0.642 | 0.768 | 0.895 | 1.022 | 1.149 | 1.277 | 1.404 | 1.531 |
| min | 0.237 | 0.298 | 0.36 | 0.421 | 0.482 | 0.605 | 0.729 | 0.852 | 0.976 | 1.098 | 1.223 | 1.345 | 1.47 | |
| s | max | 0.438 | 0.5 | 0.562 | 0.625 | 0.75 | 0.938 | 1.125 | 1.312 | 1.5 | 1.688 | 1.875 | 2.062 | 2.25 |
| min | 0.425 | 0.484 | 0.544 | 0.603 | 0.725 | 0.906 | 1.088 | 1.269 | 1.45 | 1.631 | 1.812 | 1.994 | 2.175 | |
| e | max | 0.505 | 0.577 | 0.650 | 0.722 | 0.866 | 1.083 | 1.299 | 1.516 | 1.732 | 1.949 | 2.165 | 2.382 | 2.598 |
| min | 0.484 | 0.552 | 0.620 | 0.687 | 0.826 | 1.033 | 1.240 | 1.447 | 1.653 | 1.859 | 2.066 | 2.273 | 2.480 | |
| k | max | 0.188 | 0.235 | 0.268 | 0.316 | 0.364 | 0.444 | 0.524 | 0.604 | 0.7 | 0.78 | 0.876 | 0.94 | 1.036 |
| min | 0.15 | 0.195 | 0.226 | 0.272 | 0.302 | 0.378 | 0.455 | 0.531 | 0.591 | 0.658 | 0.749 | 0.81 | 0.902 | |
| r | max | 0.030 | 0.030 | 0.030 | 0.030 | 0.030 | 0.060 | 0.060 | 0.060 | 0.090 | 0.090 | 0.090 | 0.090 | 0.090 |
| min | 0.010 | 0.010 | 0.010 | 0.010 | 0.010 | 0.020 | 0.020 | 0.020 | 0.030 | 0.030 | 0.030 | 0.030 | 0.030 | |
| b | Ref L≤6 | 0.75 | 0.875 | 1 | 1.125 | 1.25 | 1.5 | 1.75 | 2 | 2.25 | 2.5 | 2.75 | 3 | 3.25 |
| Ref L＞6 | 1 | 1.125 | 1.25 | 1.375 | 1.5 | 1.75 | 2 | 2.25 | 2.5 | 2.75 | 3 | 3.25 | 3.5 | |
Technical Data provided by Fastener Planet
| Thread Size (d) | 1-5/8 | 1-3/4 | 1-7/8 | 2 | 2-1/4 | 2-1/2 | 2-3/4 | 3 | 3-1/4 | 3-1/2 | 3-3/4 | 4 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PP | UNC | 5 | – | 4-1/2 | 4-1/2 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
| UNF | – | – | – | – | – | – | – | – | – | – | – | – | |
| 8-UN | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | |
| ds | max | 1.658 | 1.785 | 1.912 | 2.039 | 2.305 | 2.559 | 2.827 | 3.081 | 3.335 | 3.589 | 3.858 | 4.111 |
| min | 1.591 | 1.716 | 1.839 | 1.964 | 2.214 | 2.461 | 2.711 | 2.961 | 3.21 | 3.461 | 3.726 | 3.975 | |
| s | max | 2.438 | 2.625 | 2.812 | 3 | 3.375 | 3.75 | 4.125 | 4.5 | 4.875 | 5.25 | 5.625 | 6 |
| min | 2.356 | 2.538 | 2.719 | 2.9 | 3.262 | 3.625 | 3.988 | 4.35 | 4.712 | 5.075 | 5.437 | 5.8 | |
| e | max | 2.815 | 3.031 | 3.248 | 3.464 | 3.897 | 4.330 | 4.763 | 5.196 | 5.629 | 6.062 | 6.495 | 6.928 |
| min | 2.616 | 2.893 | 3.099 | 3.306 | 3.719 | 4.133 | 4.546 | 4.959 | 5.372 | 5.786 | 6.198 | 6.612 | |
| k | max | 1.116 | 1.196 | 1.276 | 1.388 | 1.548 | 1.708 | 1.869 | 2.06 | 2.251 | 2.38 | 2.572 | 2.764 |
| min | 0.978 | 1.054 | 1.13 | 1.175 | 1.327 | 1.479 | 1.632 | 1.815 | 1.936 | 2.057 | 2.241 | 2.424 | |
| r | max | 0.090 | 0.120 | 0.120 | 0.120 | 0.19 | 0.190 | 0.190 | 0.190 | 0.190 | 0.190 | 0.190 | 0.190 |
| min | 0.030 | 0.040 | 0.040 | 0.040 | 0.06 | 0.060 | 0.060 | 0.060 | 0.060 | 0.060 | 0.060 | 0.060 | |
| b | Ref L≤6 | 3.5 | 3.75 | 4 | 4.25 | 4.75 | 5.25 | 5.75 | 6.25 | 6.75 | 7.25 | 7.75 | 8.25 |
| Ref L＞6 | 3.75 | 4 | 4.25 | 4.5 | 5 | 5.5 | 6 | 6.5 | 7 | 7.5 | 8 | 8.5 | |
Technical Data provided by Fastener Planet