Every value on TorqueSpec is calculated from published engineering standards — never copied from other websites. Here's exactly how.
T = K × D × F
T — Tightening torque
K — Nut factor (friction coefficient). Depends on surface condition: dry steel = 0.20, oiled = 0.15, zinc plated = 0.18, waxed = 0.10, MoS₂ = 0.12, galvanized = 0.25. Values per VDI 2230.
D — Nominal bolt diameter
F — Clamp load = 75% of proof load. Proof load = proof stress × tensile stress area. The 75% factor provides a safety margin below the bolt's proof load, which is standard practice in non-critical fastener applications.
M10 × 1.5 mm, Class 8.8, dry steel:
Proof stress = 580 MPa (ISO 898-1 Table 4)
Stress area = 58.0 mm² (ISO 898-1 Annex A)
Proof load = 580 × 58.0 = 33,640 N
Clamp load F = 0.75 × 33,640 = 25,230 N
T = 0.20 × 0.010 m × 25,230 N = 50.5 N·m
ISO 898-1:2013
Mechanical properties of fasteners made of carbon steel and alloy steel — Bolts, screws and studs with specified property classes — Coarse thread and fine pitch thread. Provides proof stress, tensile strength, and yield strength for metric property classes 4.6 through 12.9.
SAE J429 (2014)
Mechanical and Material Requirements for Externally Threaded Fasteners. Defines proof load, tensile strength, and yield strength for SAE grades 2, 5, and 8 imperial fasteners.
ISO 261 / ISO 262
ISO general purpose metric screw threads — General plan and selected sizes. Defines thread geometry, pitch, and stress areas for metric fasteners.
ASME B1.1
Unified Inch Screw Threads (UN, UNR, and UNJ Thread Form). Defines thread geometry and stress areas for imperial (unified) fasteners.
VDI 2230 (2015)
Systematic Calculation of Highly Stressed Bolted Joints. Provides K-factor (nut factor) values for various surface conditions and lubrication states.
The nut factor K is the single most important variable in torque calculation. It accounts for friction in the threads and under the bolt head.
| Surface Condition | K Factor | Description |
|---|---|---|
| Waxed | 0.10 | Wax-coated fasteners, lowest friction |
| MoS₂ | 0.12 | Molybdenum disulfide anti-seize compound |
| Oiled | 0.15 | Machine oil or light lubricant on threads |
| Zinc Plated | 0.18 | Electroplated zinc coating |
| Plain / Dry | 0.20 | Uncoated steel, as-received condition |
| Galvanized | 0.25 | Hot-dip galvanized, highest friction |
Our calculated values have been cross-referenced against published torque tables from multiple independent sources:
Portland Bolt — manufacturer torque tables for imperial grades
Fastenal — engineering reference torque data
Bolt Depot — fastener specification charts
Fractory — metric bolt torque reference tables
All values fall within ±2% of published references, confirming the accuracy of our calculation methodology.
The torque values on TorqueSpec are calculated from published engineering standards and are intended for general reference only. They should not be used as the sole basis for critical, safety-related, or structural applications. Always consult the fastener manufacturer's specifications, the applicable design standard (e.g., VDI 2230 for systematic bolted joint design), and a qualified engineer when designing bolted connections where failure could result in injury, death, or significant property damage. Actual torque requirements may vary based on joint geometry, gasket materials, temperature, vibration, and other application-specific factors not accounted for in the simplified T = K × D × F formula.
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