The shear strength of a bolt is the highest sideways force that a bolt can withstand before breaking apart along its cross-section.
Incorrect calculation of the shear strength of bolts can lead to fastener failure. This results in damage and even dangerous accidents.
This article describes the definition of shear strength of bolts, calculating methods, and bolt grade selection for the particular load in a joint.
What Is Bolt Shear Strength?
A force exerted on the bolt connecting two pieces that tends to make them slide relative to one another is experienced as shear.
In shear, the load is applied perpendicular to the axis of the bolt, unlike tension, where the load is applied parallel to the axis of the bolt.
For most bolts, there is no specified shear strength. The shear strength of a bolt is calculated from the tensile strength of the bolt using a well-known ratio.
Using the well-accepted equation, consistent with AISC and Eurocode 3 specifications, the ratio of shear to minimum ultimate tensile strength is set at about 60%.
Shear Strength vs Tensile Strength: Key Differences
These two types of strengths measure different methods of failure.
Tensile strength measures the resistance to fracture of a bolt under axial tensile stress. Meanwhile, shear strength measures the resistance to shear deformation of the shank of the bolt.
Both values matter, but in different joint configurations. A bolted flange under internal pressure loads bolts in tension.
A lap joint or a bracket bolted to a beam loads bolts in shear. Many real assemblies combine both, which is why engineers use interaction formulas when combined loading applies.
For procurement purposes, the bolt tensile strength chart is the primary reference. Shear capacity is then derived from that value rather than specified independently on most bolt datasheets.
Bolt Shear Strength by Grade
The table below shows minimum tensile strength, derived shear strength, and typical applications for common metric and imperial bolt grades. Shear values are calculated at 60 percent of minimum tensile strength.
| Grade | Standard | Min. Tensile (MPa) | Derived Shear (MPa) | Typical Use |
|---|---|---|---|---|
| 4.8 | ISO 898-1 | 420 | 252 | Light structural, general assembly |
| 8.8 | ISO 898-1 | 800 | 480 | Structural steel, machinery |
| 10.9 | ISO 898-1 | 1040 | 624 | Automotive, heavy machinery |
| 12.9 | ISO 898-1 | 1220 | 732 | High-load, precision assemblies |
| Grade 5 | SAE J429 | 827 | 496 | General industrial, imperial |
| Grade 8 | SAE J429 | 1034 | 620 | Structural, drivetrain, high-stress |
| A325 | ASTM F3125 | 827 | 496 | Structural steel connections |
| A490 | ASTM F3125 | 1034 | 620 | Heavy structural, bridges |
This bolt strength chart covers the grades used most frequently in industrial and structural applications.
For a more detailed bolt tensile strength chart across all sizes and sub-grades, refer to ISO 898-1 for metric and ASTM F3125 for imperial structural grades.
How to Calculate Bolt Shear Strength
The basic formula for single shear capacity of a bolt is:
Shear Capacity = 0.6 x Fub x As
Where Fub is the minimum ultimate tensile strength in MPa, and As is the stress area of the bolt in square millimeters.
Example
An M16 Grade 10.9 bolt has a stress area of 157 mm² and a minimum tensile strength of 1,040 MPa.
Shear Capacity = 0.6 x 1,040 x 157 = 97,968 N, approximately 98 kN per bolt.
That figure represents the theoretical single-shear capacity of one bolt before applying any safety factor.
In structural design, Eurocode 3 applies a partial safety factor of 1.25. This reduces the design shear resistance to approximately 78 kN for this bolt in practice.
For imperial bolts, the same formula applies using tensile strength in pounds per square inch (psi) and stress area in square inches.
A 1/2 inch Grade 8 bolt with a stress area of 0.1419 in² and tensile strength of 150,000 psi gives a single shear capacity of approximately 0.6 x 150,000 x 0.1419 = 12,771 lbf. That’s roughly 12.8 kips.
Single Shear vs Double Shear
The number of shear planes in a joint changes the effective capacity of each bolt significantly.
Single Shear
In a single shear joint, the bolt crosses one shear plane. A simple lap joint where two plates overlap and are connected by bolts is a typical single shear configuration. Each bolt resists the full applied load across one cross-section.
Double Shear
In a double shear joint, the bolt passes through three plates: one inner and two outer members.
This creates two shear planes, and the bolt resists load across two cross-sections simultaneously. This effectively doubles the bolt’s shear capacity for the same bolt diameter and grade.
Gusset plate connections, clevis pin joints, and some beam-to-column connections use double shear configurations to reduce bolt count or allow smaller diameter fasteners. When calculating capacity for double shear, multiply the single shear value by two.
How to Select the Right Bolt Grade for Shear Loads
- This Grade 10.9 wheel hub bolt is manufactured from high-strength steel 40Cr or 35CrMo, featuring a black oxide finish for excellent corrosion resistance and robustness.
Selecting a grade starts with calculating the design shear load per bolt, then matching it to a grade that provides adequate capacity with the required safety factor applied.
A few practical guidelines help narrow the selection:
For general structural steel connections per AISC, A325 or A490 bolts are the standard. A490 suits higher-load connections where A325 would require more bolts.
For metric structural applications under Eurocode 3, Grade 8.8 covers most standard connections. Grade 10.9 is used where joint geometry limits bolt count or diameter.
For automotive and precision machinery, high tensile bolts at Grade 10.9 or 12.9 handle vibration-intensive environments. This is where lower grades would require tighter torque control or locking features to prevent loosening.
Material matters beyond grade number. High-tensile bolts in duplex stainless or alloy steel are specified where corrosion resistance and shear capacity must both be satisfied. This is particularly in marine, chemical, and energy applications.
CNXD supplies high-strength bolts from Grade 8.8 to 12.9 in carbon steel, alloy steel, and specialty alloys. This has IATF 16949 quality documentation and full material traceability.
Custom sizes and non-standard thread forms are also available. Contact CNXD to request samples for load-bearing application evaluation.
