Heavy Hex Bolts
A heavy hex bolt is a hex head fastener distinguished by a larger head pattern than a standard finished hex bolt. The wider width across flats and corners gives the bolt greater bearing surface and a stronger head-to-body connection. This makes heavy hex bolts the required head style for several ASTM specifications where a standard hex head would not meet dimensional or strength demands, including F1554, A193, A320, and A307 Grade B. Although F3125 Grades A325, A490, and 144 also possess a heavy hex head, dimensional requirements for those fasteners are covered under the Heavy Hex Structural Bolt dimensions.
Applications
Heavy hex bolts are used to fasten wood, steel, and other construction materials across a wide span of infrastructure and building projects. Common applications include docks, bridges, highway structures, and commercial buildings, where the larger head provides added clamping and bearing performance for structural connections.
Beyond standard bolting, heavy hex bolts with forged heads are frequently used as headed anchor bolts, embedding into concrete to anchor structural steel, equipment, and other assemblies. The combination of several available grades and galvanized corrosion protection makes them well suited to demanding load-bearing and exposed environments.
Specs
Several ASTM specifications require a hex head that is larger than a standard (finished) hex head. These specifications include: A193, A320 and A307B. Although A325 and A490 bolts also require a heavy hex head, please refer to Structural Bolts for dimensional specifications, since these bolts have shorter thread lengths than standard heavy hex bolts.
Manufacturing
Portland Bolt manufactures heavy hex bolts from 1/2” diameter through 2-1/2” diameter in most ASTM, AASHTO, and SAE specifications, covering a broad grade range that includes A307B, F1554, A325, A490, A193, and A320. Available finishes are plain black and hot-dip galvanized. All head dimensions conform to ASME B18.2.1. Note that while A325, A490, and Grade 144 structural bolts also use a heavy hex head, those are treated as structural bolts because they carry shorter thread lengths than standard heavy hex bolts and possess a full body diameter.
Production runs through the core in-house processes of cutting, heading, threading, and hot-dip galvanizing. Heads are forged to the oversized heavy hex pattern, and threads are applied to standard length formulas: for bolts 6” and shorter, thread length equals two times the diameter plus ¼”, and for bolts longer than 6”, thread length equals two times the diameter plus ½”. Special tooling can be created to forge bolt heads carrying a company name or logo. Portland Bolt also stocks A325 heavy hex structural bolts, and domestic manufacturing since 1912 supports full certification and testing on these fasteners.
Stock
Portland Bolt stocks A325 Heavy Hex Structural Bolts.
Standard Thread Lengths
Bolt lengths ≤ 6″: Thread length = (2 X diameter) + 1/4″
Bolt lengths > 6″: Thread length = (2 X diameter) + 1/2″
Heavy Hex Dimensions
| Bolt Diameter | D | F | C | H | |||||
|---|---|---|---|---|---|---|---|---|---|
| Body Diameter | Width Across Flats | Width Across Corners | Height | ||||||
| Max | Basic | Max | Min | Max | Min | Basic | Max | Min | |
| 1⁄2 | 0.515 | 7⁄8 | 0.875 | 0.850 | 1.010 | 0.969 | 11⁄32 | 0.364 | 0.302 |
| 5⁄8 | 0.642 | 11⁄16 | 1.062 | 1.031 | 1.227 | 1.175 | 27⁄64 | 0.444 | 0.378 |
| 3⁄4 | 0.768 | 11⁄4 | 1.250 | 1.212 | 1.443 | 1.383 | 1⁄2 | 0.524 | 0.455 |
| 7⁄8 | 0.895 | 17⁄16 | 1.438 | 1.394 | 1.660 | 1.589 | 37⁄64 | 0.604 | 0.531 |
| 1 | 1.022 | 15⁄8 | 1.625 | 1.575 | 1.876 | 1.796 | 43⁄64 | 0.700 | 0.591 |
| 11⁄8 | 1.149 | 113⁄16 | 1.812 | 1.756 | 2.093 | 2.002 | 3⁄4 | 0.780 | 0.658 |
| 11⁄4 | 1.277 | 2 | 2.00 | 1.938 | 2.309 | 2.209 | 27⁄32 | 0.876 | 0.749 |
| 13⁄8 | 1.404 | 23⁄16 | 2.188 | 2.119 | 2.526 | 2.416 | 29⁄32 | 0.940 | 0.810 |
| 11⁄2 | 1.531 | 23⁄8 | 2.375 | 2.300 | 2.742 | 2.622 | 1 | 1.036 | 0.902 |
| 15⁄8 | 1.658 | 29⁄16 | 2.562 | 2.481 | 2.959 | 2.829 | 13⁄32 | 1.116 | 0.978 |
| 13⁄4 | 1.785 | 23⁄4 | 2.750 | 2.662 | 3.175 | 3.035 | 15⁄32 | 1.196 | 1.054 |
| 17⁄8 | 1.912 | 215⁄16 | 2.938 | 2.844 | 3.392 | 3.242 | 11⁄4 | 1.276 | 1.130 |
| 2 | 2.039 | 31⁄8 | 3.125 | 3.025 | 3.608 | 3.449 | 111⁄32 | 1.388 | 1.175 |
| 21⁄4 | 2.305 | 31⁄2 | 3.500 | 3.388 | 4.041 | 3.862 | 11⁄2 | 1.548 | 1.327 |
| 21⁄2 | 2.559 | 37⁄8 | 3.875 | 3.750 | 4.474 | 4.275 | 121⁄32 | 1.708 | 1.479 |
Dimensions per ASME B18.2.1 | |||||||||
FAQs
A heavy hex bolt is a hex head fastener with a larger head than a standard finished hex bolt, offering a greater width across flats and wider corners. This larger pattern provides more bearing surface and is required by several ASTM specifications for structural and high-strength applications.
The main difference is head size. A heavy hex bolt has a larger width across flats and wider width across corners than a standard finished hex bolt of the same diameter. This gives heavy hex bolts more bearing surface and makes them the required head style for certain ASTM specifications.
Portland Bolt manufactures heavy hex bolts from ½” diameter through 2-1/2” diameter in most ASTM, AASHTO, and SAE specifications. Logos or company names can also be applied to the bolt heads with special tooling.
Portland Bolt offers heavy hex bolts in a range of grades, including A307B, F1554, F3125, Grades A325, A490, and 144, A193, and A320, covering general construction, anchor bolt, structural, and high-temperature or low-temperature service needs.
Heavy hex bolts from Portland Bolt are available in plain black (uncoated) and hot-dip galvanized finishes. Hot-dip galvanizing provides corrosion protection for exposed and outdoor structural applications and is applied in our state-of-the-art hot-dip galvanizing line.
Several ASTM specifications require a heavy hex head that is larger than a standard hex head, including A193, A320, and A307 Grade B. F3125 Grades A325, A490, and 144 bolts also use a heavy hex head, but those are classified as structural bolts because they have shorter thread lengths and a full body diameter.
For heavy hex bolts 6” long or shorter, the thread length equals two times the diameter plus 1/4”. For bolts longer than 6”, the thread length equals two times the diameter plus 1/2”
Yes. Heavy hex bolts with forged heads are commonly used as headed anchor bolts, embedding into concrete to secure structural steel, equipment, and other assemblies. The forged head provides the bearing needed for anchoring.
Heavy hex bolt head dimensions, including body diameter, width across flats, width across corners, and head height, conform to ASME B18.2.1.
Yes. Portland Bolt can create special tooling to forge bolt heads that carry a company name and/or logo.