ASME B18.2.1 Square Head Bolts
ASME B18.2.1 Square Head Bolts are designed with a four-sided head that provides multiple flat surfaces for wrench engagement. This head configuration allows the bolt to be tightened or loosened with suitable tools and can provide practical advantages where a conventional hexagonal head is not preferred. The square head also offers a straightforward visual profile and can be useful in assemblies where the fastener head needs to be gripped securely during installation. The bolt can be used with a matching nut or threaded component to form a conventional bolted connection.
ASME B18.2.1 square head bolts are available in inch diameters and lengths, with different thread configurations and material or surface finish options available according to the required specification. Custom sizes, materials, and finishes can also be supplied for specific drawings or applications.
Specification:
ASME B18.2.1 square head bolts are manufactured according to the dimensional requirements for inch-series square head bolts, covering key dimensions such as nominal diameter, head width, head height, bolt length, and other related features. The bolts use Unified inch threads, with UNC and UNF thread configurations available according to the required application. Thread requirements are specified in accordance with ASME B1.1, while head and bolt dimensions are controlled according to ASME B18.2.1.
Material and mechanical properties are selected according to the required fastener grade. Carbon steel and alloy steel bolts can be supplied in common SAE J429 grades such as Grade 2, Grade 5, and Grade 8, with tensile strength, yield strength, hardness, and other mechanical requirements determined by the applicable grade and diameter. Stainless steel versions can be supplied according to ASTM F593, with the applicable alloy group and material condition determining the required mechanical properties.
| Item | Specification |
|---|---|
| Product Type | Square Head Bolt |
| Dimensional Standard | ASME B18.2.1 |
| Thread | Unified Inch Thread |
| Thread Type | UNC/UNF |
| Thread Standard | ASME B1.1 |
| Head Type | Square Head |
| Size Range | 1/4“- 1-1/2” |
| Mechanical Proeprty Standard | SAE J429,A307,F593 |
| Material | Carbon Steel, Alloy Steel, Stainless Steel |
| Surface Treatment | Zinc Plated,Black Oxidation,Hot Dip Galvanized,Dacromet,Bright Finish |
| Inspection | Dimensional,Thread,Mechanical Proeprty,Coating |
- RELATED BOLT LISTS:
- ASME B 18.31.5 HRA Hook Bolts
- ASTM A394 HDG Tower Bolts
- ASTM A354 Hex Bolts
- ASME B 18.2.1 Square Head Bolts
- ASME/ANSI B 18.5 Round Head Square Neck Bolts
- ASME/ANSI B18.5 T- Head Bolts
- ASME/ANSI B18.2.1 Hex Head Flange Bolts
- ASME/ANSI B18.5 80°Slotted Countersunk Head Bolts
- ASME/ANSI B18.2.1 Hex Cap Bolts
- A307 Hex Head Bolts
Dimension Chart of ASME B 18.2.1 Square Head Bolts:
The dimension chart below provides the main dimensional information for ASME B18.2.1 square head bolts, including nominal diameter, bolt length, square head width, and head height. Dimensions are based on the applicable inch-series specification, while thread size and pitch are selected according to the required UNC or UNF configuration.
Available sizes and lengths can vary according to the selected material, thread configuration, and production requirements. Custom lengths and other dimensional requirements can be manufactured according to customer drawings or project specifications.
| Thread Diameter | 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 |
| P | 20|28|32 | 18|24|32 | 16|24|32 | 14|20|28 | 13|20|28 | 11|18|24 | 10|16|20 | 9|14|20 | 8|12|20 | 7|12|18 | 7|12|18 | 6|12|18 | 6|12|18 |
| 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 |
| ds 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 | 0.375 | 0.5 | 0.562 | 0.625 | 0.75 | 0.938 | 1.125 | 1.312 | 1.5 | 1.688 | 1.875 | 2.062 | 2.25 |
| s min | 0.362 | 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 | 0.53 | 0.707 | 0.795 | 0.884 | 1.061 | 1.326 | 1.591 | 1.856 | 2.121 | 2.386 | 2.652 | 2.917 | 3.182 |
| e min | 0.498 | 0.665 | 0.747 | 0.828 | 0.995 | 1.244 | 1.494 | 1.742 | 1.991 | 2.239 | 2.489 | 2.738 | 2.986 |
| k max | 0.188 | 0.22 | 0.268 | 0.316 | 0.348 | 0.444 | 0.524 | 0.62 | 0.684 | 0.78 | 0.876 | 0.94 | 1.036 |
| k min | 0.156 | 0.186 | 0.232 | 0.278 | 0.308 | 0.4 | 0.476 | 0.568 | 0.628 | 0.72 | 0.812 | 0.872 | 0.964 |
| r max | 0.03 | 0.03 | 0.03 | 0.03 | 0.03 | 0.06 | 0.06 | 0.06 | 0.09 | 0.09 | 0.09 | 0.09 | 0.09 |
| r min | 0.01 | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.02 | 0.02 | 0.03 | 0.03 | 0.03 | 0.03 | 0.03 |
Application of ASME B 18.2.1 Square Head Bolts:
Machinery & Equipment
Square head bolts are suitable for machinery frames, equipment assemblies, brackets, guards, and fabricated components where a traditional square-headed fastener is specified. The four-sided head provides accessible flat surfaces for wrench tightening during assembly.
Metal Fabrication
They can be used in fabricated steel components, frames, supports, brackets, and general metal assemblies where inch-series fasteners are required. Different diameters and lengths allow the bolt to be selected according to the joint design.
Agricultural & Industrial Equipment
ASME B18.2.1 square head bolts are also suitable for agricultural machinery, industrial equipment, trailers, structural components, and repair or replacement assemblies using American inch-based fasteners.