A325 Bolts — Strength and Allowable Capacity
The default high-strength structural bolt for building steel. Now published as ASTM F3125 Grade A325, though every shop drawing and mill ticket in the field still says A325.
Specified strengths
- Standard: ASTM F3125 Grade A325
- Tensile strength Fu: 120 ksi
- Nominal tensile stress Fnt: 90 ksi
- Nominal shear stress Fnv: 54 ksi threads included (N); 68 ksi threads excluded (X)
Allowable capacity by diameter
| Diameter | Ab (in²) | A325 tension (kip) | A325 shear (kip) |
|---|---|---|---|
| 1/2" | 0.196 | 8.8 | 5.3 |
| 5/8" | 0.307 | 13.8 | 8.3 |
| 3/4" | 0.442 | 19.9 | 11.9 |
| 7/8" | 0.601 | 27.1 | 16.2 |
| 1" | 0.785 | 35.3 | 21.2 |
| 1-1/8" | 0.994 | 44.7 | 26.8 |
| 1-1/4" | 1.227 | 55.2 | 33.1 |
| 1-1/2" | 1.767 | 79.5 | 47.7 |
Allowable Stress Design (ASD), Ω = 2.00. Bearing-type, snug-tight, one shear plane, threads included (N), nominal shank area. For end-loaded connections with a fastener pattern longer than 38 in., multiply shear by 0.833 per American Institute of Steel Construction (AISC) 360 Table J3.2. Bearing, tearout, block shear, net section, prying and bolt interaction are separate checks. Fu is a material minimum, not an allowable stress.
Where it is used
- Beam-to-column and beam-to-beam shear connections, snug-tight bearing type.
- Pretensioned and slip-critical joints where called out.
- Plain, hot-dip or mechanically galvanized, or weathering (Type 3). Order as an F3125 assembly with matching nuts and washers; coating and type change the installation requirements. F1852 is the twist-off equivalent.
- Reuse per Research Council on Structural Connections (RCSC): galvanized A325 never; plain A325 only with the engineer's approval.
Identifying it in the field
Head marked "A325" plus the manufacturer's mark (F3125). Three radial lines may also appear on heavy-hex heads. Type 3 (weathering): "A325" underlined.
Related
- Bolt Tensile & Shear Capacity Calculator
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- Fillet Weld Strength Calculator
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- Beam Shear, Moment and Deflection Diagram Calculator
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