Bolt Specifications & Grades Reference — A325, A490, 8.8, 10.9

Quick reference for structural bolt specifications across four major design codes: AISC 360 (US), EN 1993-1-8 (Europe/UK), AS 4100 (Australia), and CSA S16:24 (Canada). Includes bolt grade strengths, dimensions, tightening requirements, and material specifications.

PRELIMINARY — NOT FOR CONSTRUCTION. All results are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.

Bolt Grade Comparison by Code

| Code | Common Grades | Tensile Strength Fu (MPa) | Yield Strength Fy (MPa) | Spec Reference | | ---

• | ------------- | ------------------------- | ----------------------- | -------------- | | AISC 360 (US) | A325 (ASTM F3125) | 830 (1 in and under), 725 (over 1 in) | 635, 560 | Table J3.2 | | AISC 360 (US) | A490 (ASTM F3125) | 1040 | 895 | Table J3.2 | | AISC 360 (US) | F1852 (twist-off) | Same as A325 | Same as A325 | ASTM F1852 | | AISC 360 (US) | F2280 (twist-off) | Same as A490 | Same as A490 | ASTM F2280 | | EN 1993-1-8 (EU/UK) | 4.6 | 400 | 240 | EN 15048 | | EN 1993-1-8 (EU/UK) | 5.6 | 500 | 300 | EN 15048 | | EN 1993-1-8 (EU/UK) | 6.8 | 600 | 480 | EN 15048 | | EN 1993-1-8 (EU/UK) | 8.8 | 800 | 640 | EN 14399 / ISO 898-1 | | EN 1993-1-8 (EU/UK) | 10.9 | 1000 | 900 | EN 14399 / ISO 898-1 | | AS 4100 (AU) | 4.6/S | 400 | 240 | AS 1252 / AS/NZS 1252 | | AS 4100 (AU) | 8.8/S | 830 | 660 | AS 1252 / AS/NZS 1252 | | AS 4100 (AU) | 10.9/S | 1040 | 940 | AS 1252 / AS/NZS 1252 | | CSA S16 (CA) | A325M / A325 | 830 (≤1 in), 725 (>1 in) | 635, 560 | CSA G40.20 / ASTM F3125 | | CSA S16 (CA) | A490M / A490 | 1040 | 895 | CSA G40.20 / ASTM F3125 |

Bolt Dimensions — Metric Series (EN 14399 / ISO 898-1)

Bolt Dimensions — Imperial Series (ASTM F3125)

Bolt Pretension Requirements

AISC 360 (Table J3.1)

Pretension is required in the following connection types:

• Slip-critical connections (all diameters)
• Moment connections (fully restrained)
• Tension connections (direct load in bolt axis)
• Columns splices (when required by design)
• Bracing connections (seismic force-resisting)

Minimum bolt pretension per AISC Table J3.1:

EN 1993-1-8 (Clause 3.6.1)

Preloaded bolts (categories E and F) require:

• Fp,C = 0.7 x fub x As (nominal pretension force)
• Minimum bolt class: 8.8 for preloaded assemblies
• Calibrated torque wrench or combined method for tightening
• Direct tension indicator (DTI) washers permitted

AS 4100 (Table 15.2.1)

Preloaded bolts (8.8/S and 10.9/S) minimum bolt tension:

• M16: 95 kN (8.8/S), 125 kN (10.9/S)
• M20: 145 kN (8.8/S), 195 kN (10.9/S)
• M24: 210 kN (8.8/S), 280 kN (10.9/S)
• M30: 335 kN (8.8/S), 445 kN (10.9/S)

CSA S16:24

Same as AISC — A325M/A490M pretension per CSA S16:24 Clause 22.3.

Bolt Shear Strength Summary

AISC 360-22 Table J3.2 (LRFD phi = 0.75)

EN 1993-1-8 Table 3.4

Note: gamma_M2 = 1.25 (EN 1993-1-8). For 10.9 bolts, the coefficient is 0.5 instead of 0.6 to account for reduced ductility.

AS 4100 Clause 15.3

phi = 0.80 for AS 4100 bolt shear capacity.

CSA S16:24 Clause 13.12.1.2

phi_b = 0.80. Note that CSA S16 uses Fu directly rather than Fnv.

Bolt Tensile Strength Summary

AISC 360-22 Table J3.2

EN 1993-1-8

Ft,Rd = k2 x fub x As / gamma_M2 (Table 3.4)

• k2 = 0.9 for standard bolts (1.0 for countersunk)
• gamma_M2 = 1.25

AS 4100

Ntf = 0.80 x fuf x An (Clause 15.2) phi = 0.80

CSA S16:24

Tr = 0.75 x phi_b x Ab x Fu (Clause 13.12.1.3) phi_b = 0.80

Tightening Methods

Bolt Specifications by Application

Material Specification Details

A325 / A490 (ASTM F3125)

• Grade A325: heat-treated medium-carbon steel (or alloy steel)
• Grade A490: quenched and tempered alloy steel
• Marking: A325 (three radial lines), A490 (six radial lines)
• Galvanizing: A325 may be hot-dip galvanized; A490 NOT permitted to be galvanized (hydrogen embrittlement risk)
• Replacement A490 bolts: ASTM F304M (if galvanized needed)

Grade 8.8 / 10.9 (ISO 898-1 / EN 14399)

• Grade 8.8: quenched and tempered carbon steel
• Grade 10.9: quenched and tempered alloy steel
• Marking: 8.8 (distinctive head marking), 10.9 (distinctive head marking)
• Surface finish: as-rolled or phosphate coated
• HRC: 22-32 (8.8), 32-39 (10.9)
• EN 14399 requires specific washer assemblies for preloaded connections

AS 1252 (Australia)

• Grade 4.6/S: low-carbon steel bolting
• Grade 8.8/S: carbon steel quenched and tempered
• Grade 10.9/S: alloy steel quenched and tempered
• S suffix indicates structural grade per AS 1252
• Galvanized 8.8/S bolts require hydrogen embrittlement relief baking

Frequently Asked Questions

What is the difference between A325 and Grade 8.8 bolts? A325 (ASTM F3125) has minimum Fu = 120 ksi (830 MPa) for diameters up to 1 inch, while Grade 8.8 has Fu = 800 MPa. They are broadly equivalent, but A325 uses imperial dimensions (UNC thread) while Grade 8.8 bolts are metric (ISO thread). The tensile stress area differs: a 3/4 in A325 has 0.334 in^2, while an M20 Grade 8.8 has 245 mm^2. Always verify equivalent grades with the project specification.

When should I use 10.9 instead of 8.8 bolts? Use 10.9 bolts when bolt count is constrained by geometry (narrow flanges, limited joint width), when high strength is required in tension, or to reduce the number of bolt rows. However, 10.9 bolts have lower ductility (Fv,Rd coefficient = 0.5 vs 0.6 for 8.8 per EN 1993-1-8), so they are less forgiving in connections with significant deformation demand.

How do I select between bearing-type and slip-critical connections? Bearing-type connections are standard for most applications — bolts bear against the connected plies. Slip-critical connections are required where slip of the joint would cause unacceptable deformation or where the joint is subject to load reversal (wind or seismic bracing). Slip-critical bolts are preloaded to develop friction between faying surfaces, and the slip resistance depends on surface treatment (Class A: 0.33, Class B: 0.50 slip coefficient).

What bolt grade should I use for anchor bolts? Anchor bolts are typically specified as ASTM F1554 Grade 36 (36 ksi yield), Grade 55 (55 ksi yield), or Grade 105 (105 ksi yield). F1554 Grade 36 is the most common for general construction. For metric applications, use Grade 4.6 or 5.6. Avoid using A325 or A490 as anchor bolts — they are not designed for embedment in concrete and lack the corrosion protection needed for foundation connections.

How does bolt grade selection affect connection economy? Higher-grade bolts (A490, 10.9) cost 30-50% more per bolt than standard grades (A325, 8.8) but may reduce the number of bolts required by 25-30%. The net connection cost can be lower when fewer bolts means smaller gusset plates, less edge distance, and simpler detailing. For small connections (2-4 bolts), the material cost difference is negligible — use standard grades. For large connections (10+ bolts), the cost trade-off should be calculated.

What is the correct thread length for structural bolts? Standard structural bolts are available in several thread length options per ASTM A325 and A563. For snug-tight joints, threads are permitted in the shear plane. For slip-critical or preloaded joints, the thread length must be sufficient to allow the nut to be installed but the unthreaded portion should extend past the shear plane when possible. EN 14399 specifies thread lengths for structural bolts to ensure proper engagement.

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Related Pages

• AISC Bolt Capacity Table — design capacities for A325 and A490
• Bolt Grades Reference — detailed grade properties and cross-references
• Bolt Torque Chart — tightening torque values
• Bolt Spacing & Edge Distance — minimum requirements per code
• Steel Grades Reference — connected material properties
• Steel Fy and Fu Table — yield and tensile strengths for plates

Design Resources

Calculator tools

• Bolted Connection Calculator
• Bolt Torque Calculator
• Gusset Plate Calculator
• Splice Connection Calculator

Design guides

• Bolted Connection Checklist
• Bolt Grade Selection Guide
• Bolt Torque Worked Example
• EN 1993 Bolted Connection Example

Disclaimer (educational use only)

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