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Square head machine bolts were the industry standard prior to hex bolts gaining prominence. Square bolts are now most commonly used for aesthetic purposes to provide a rustic look in a new structure or to match existing fasteners in an older structure. Square lag screws are also used for these purposes.
Cross arm or machine bolts are commonly supplied for the utility industry and included an added cone point.
Portland Bolt manufactures square bolts from 1/2" diameter through 2” diameter in most ASTM, AASHTO, and SAE specifications. Special tooling can be created to produce nonstandard head dimensions or bolt heads with your company’s name and/or logo.
Portland Bolt does not stock any square head bolts. However, imported sizes through 1” in diameter and 12” in length are often readily available in the marketplace. Portland Bolt can typically provide these sizes within a couple of days.
Bolt lengths < 6”: Thread length = (2 X diameter) + 1/4”
Bolt lengths > 6”: Thread length = (2 X diameter) + 1/2”
| Bolt Diameter | D | F | C | H | |||||
|---|---|---|---|---|---|---|---|---|---|
| Body Diameter | Width Across Flats | Width Across Corners | Height | ||||||
| Max | Basic | Max | Min | Max | Min | Basic | Max | Min | |
| 3/8 | 0.388 | 9/16 | 0.562 | 0.544 | 0.795 | 0.747 | 1/4 | 0.268 | 0.232 |
| 1/2 | 0.515 | 3/4 | 0.750 | 0.725 | 1.061 | 0.995 | 21/64 | 0.348 | 0.308 |
| 5/8 | 0.642 | 15/16 | 0.938 | 0.906 | 1.326 | 1.244 | 27/64 | 0.444 | 0.400 |
| 3/4 | 0.768 | 1-1/8 | 1.125 | 1.088 | 1.591 | 1.494 | 1/2 | 0.524 | 0.476 |
| 7/8 | 0.895 | 1-5/16 | 1.312 | 1.269 | 1.856 | 1.742 | 19/32 | 0.620 | 0.568 |
| 1 | 1.022 | 1-1/2 | 1.500 | 1.450 | 2.121 | 1.991 | 21/32 | 0.684 | 0.628 |
| 1-1/8 | 1.149 | 1-11/16 | 1.688 | 1.631 | 2.386 | 2.239 | 3/4 | 0.780 | 0.720 |
| 1-1/4 | 1.277 | 1-7/8 | 1.875 | 1.812 | 2.652 | 2.489 | 27/32 | 0.876 | 0.812 |
| 1-3/8 | 1.404 | 2-1/16 | 2.062 | 1.994 | 2.917 | 2.738 | 29/32 | 0.940 | 0.872 |
| 1-1/2 | 1.531 | 2-1/4 | 2.250 | 2.175 | 3.182 | 2.986 | 1 | 1.036 | 0.964 |
| 1-3/4* | 2-9/16 | 1-3/16 | |||||||
| 2* | 2-15/16 | 1-5/16 | |||||||
Dimensions per ASME B18.2.1 1996
* ASME only defines head dimensions up to 1-1/2". Dimensions for 1-3/4 and 2" are approximate and not covered under the ASME dimensional specifications.
