ASTM F3125 A325 structural bolts are quenched and tempered high-strength fasteners for structural steel connections. Under the current ASTM F3125/F3125M-26 specification, Grade A325 identifies the inch-series heavy hex style with 120 ksi minimum tensile strength and nominal diameters from 1/2 through 1-1/2 inches. The former standalone ASTM A325 specification was consolidated into ASTM F3125, while A325 remains the familiar grade designation and head marking. Typical assemblies pair the bolt with a compatible heavy hex nut and hardened structural washer selected for the bolt type, coating, and connection requirements.
Product Overview and Key Features
Grade A325 heavy hex bolts are intended for structural connections rather than general-purpose machine fastening. Their larger head provides structural bearing and wrenching geometry, while controlled mechanical properties, thread length, mating hardware, and surface condition support project installation requirements.
- 120 ksi strength level: 120 ksi minimum tensile strength and 92 ksi minimum yield strength.
- Heavy hex style: geometry follows the structural bolt dimensional requirements referenced by ASTM F3125.
- UNC inch threads: coarse Unified threads cover 1/2 through 1-1/2 inches.
- Type 1 and Type 3: general structural and weathering-steel material routes are defined.
- Matched hardware: nuts, washers, coating, and lubrication should form a compatible assembly.
ASTM F3125 A325 Structural Bolts Specifications
Specification Overview
| Item | Specification |
|---|---|
| Current standard | ASTM F3125/F3125M-26 |
| Grade and style | Grade A325, Heavy Hex |
| Nominal diameter range | 1/2 in. through 1-1/2 in. |
| Thread series | UNC inch thread |
| Minimum tensile strength | 120 ksi |
| Minimum yield strength | 92 ksi |
| Material types | Type 1 and Type 3 |
| Common matching nuts | ASTM A563 DH for Type 1; A563 DH3 for Type 3 |
| Common matching washers | ASTM F436 Type 1 for Type 1; F436 Type 3 for Type 3 |
Dimensions and Thread Details
The table shows the full Grade A325 heavy hex diameter range. TPI means threads per inch, F width across flats, H head height, and LT basic thread length for the normal partially threaded configuration.
| Nominal Thread | UNC TPI | F Basic (in.) | H Min-Max (in.) | LT Basic (in.) |
|---|---|---|---|---|
| 1/2-13 | 13 | 7/8 | 0.302-0.323 | 1.00 |
| 5/8-11 | 11 | 1-1/16 | 0.378-0.403 | 1.25 |
| 3/4-10 | 10 | 1-1/4 | 0.455-0.483 | 1.38 |
| 7/8-9 | 9 | 1-7/16 | 0.531-0.563 | 1.50 |
| 1-8 | 8 | 1-5/8 | 0.591-0.627 | 1.75 |
| 1-1/8-7 | 7 | 1-13/16 | 0.658-0.718 | 2.00 |
| 1-1/4-7 | 7 | 2 | 0.749-0.813 | 2.00 |
| 1-3/8-6 | 6 | 2-3/16 | 0.810-0.878 | 2.25 |
| 1-1/2-6 | 6 | 2-3/8 | 0.902-0.974 | 2.25 |
Standard A325 heavy hex bolts are normally partially threaded. Supplementary Requirement S1 permits A325T bolts to be fully threaded when nominal length does not exceed four times the bolt diameter. Special head geometry or thread length may require the applicable supplementary designation. Bolt length should be selected from the actual grip and connection details rather than assumed from diameter alone.
Common Materials, Grades and Surface Finishes
Material and Grade Options
Type 1 may use qualifying carbon, carbon-boron, alloy, or alloy-boron steel followed by heat treatment to achieve specified properties. Type 3 uses weathering steel chemistry and is normally matched with compatible weathering nuts and washers. The grade controls finished requirements and should not be replaced by unrelated material solely because nominal strength appears similar.
Coating and Finish Options
Common Type 1 configurations include plain finish, hot-dip galvanizing to ASTM F2329, ASTM B695 Class 55 mechanical zinc, and permitted zinc/aluminum systems. Coated assemblies require compatible nut thread allowance and lubrication. Type 3 is used with compatible weathering-steel connections. Confirm type, coating, nut, washer, and lubrication together during quotation.
Typical Applications and Selection Considerations
- Beam-to-column, splice, and bracing connections in steel buildings.
- Bridge members, platforms, gantries, and fabricated infrastructure.
- Towers, substations, utility structures, and industrial support frames.
- Heavy fabricated assemblies where project drawings specify Grade A325 structural bolting.
See Flybear’s steel construction fastening solutions for related sourcing guidance. Match diameter and length to joint grip, holes, mating hardware, surface condition, and installation method. Terms such as pretensioned or slip-critical describe joint design and installation conditions, not a different A325 manufacturing grade.
Ordering and Quality Documentation
An RFQ should identify ASTM F3125 Grade A325, Type 1 or Type 3, heavy hex style, diameter-TPI, length, coating, quantity, nut grade, washer specification, and documentation. Buyers may request material verification, dimensional inspection, thread checks, mechanical testing, coating inspection, and lot records as required. Flybear’s quality control and inspection page describes available inspection support; exact records should be agreed for the order.
Frequently Asked Questions
Is ASTM A325 still a current standalone standard?
No. The former ASTM A325 specification was consolidated into ASTM F3125. The current product designation is ASTM F3125 Grade A325. Older drawings and purchasing language may still state “A325,” so buyers should retain the grade reference while applying the current consolidated standard unless the project explicitly requires an older edition.
What sizes are covered by Grade A325 heavy hex bolts?
Grade A325 heavy hex bolts cover nominal inch diameters from 1/2 through 1-1/2 inches. Standard threads are UNC. The metric structural grade is designated separately, so inch A325 and metric A325M requirements should not be mixed when defining dimensions, threads, or purchase documentation.
What is the difference between A325 Type 1 and Type 3?
Type 1 is the general structural option using qualifying carbon or alloy steel routes. Type 3 uses weathering steel chemistry and is intended for compatible weathering-steel assemblies. Type 3 bolts should be paired with appropriate weathering nuts and washers rather than treated as a finish variation of Type 1.
Can Grade A325 structural bolts be fully threaded?
Yes, when the supplementary requirement is correctly specified. A325T bolts may be fully threaded when nominal length does not exceed four times the nominal diameter. A standard heavy hex A325 bolt should otherwise be treated as a partially threaded structural bolt, not a general-purpose fully threaded hex bolt.
Can A325 bolts be hot-dip galvanized?
Type 1 Grade A325 bolts can be hot-dip galvanized when the assembly follows the applicable ASTM coating and mating-thread requirements. The nut needs compatible thread accommodation and lubrication. Coating should therefore be ordered as part of the complete assembly specification because it affects fit and tightening behavior.
Request a Quote for Grade A325 Structural Bolting
For ASTM F3125 A325 structural bolts, send Flybear Industrial the required type, diameter, length, coating, quantity, nut grade, washer requirement, and inspection-document needs. Include drawings or a bill of materials when the connection requires special grip or installation conditions. Submit the project through the Flybear fastener RFQ page for technical review and quotation.
