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. Note: property class 8.8 has two tiers — proof stress 580 MPa for d ≤ M16, and 600 MPa for d > M16 (ISO 898-1 Table 4). Property class 9.8 is defined only for d ≤ M16.
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 |
Every bolt size-and-grade value on this site is calculated, not transcribed: T = K × D × F, with F = 0.75 × proof stress × tensile stress area. Published torque tables do not all share that basis, so we cross-reference against them to check our arithmetic and our inputs — not to match their absolute numbers.
Portland Bolt — manufacturer torque tables for imperial grades
Fastenal — engineering reference torque data
Bolt Depot — fastener specification charts
Fractory — metric bolt torque reference tables
Where a source shares our preload basis (75% of proof load) and K-factor, our values agree with it to within about 2% — the residual being rounding and small differences in the stress-area figures used. That is the case for the imperial grades checked against Portland Bolt, Fastenal and Bolt Depot.
Where a source uses a different preload basis, the two sets of numbers are not directly comparable and the gap is larger than 2%. Fractory’s metric tables are the clearest example: they are not built on the same 75%-of-proof assumption we use, so their absolute N·m figures sit on a different footing than ours even when the formula and K-factor agree. We use them to check the shape of the data — the ratios between classes, sizes and thread pitches — rather than as an absolute reference. A difference of that kind reflects a stated modelling assumption, not an error in either table.
Two further points worth stating plainly. Proof stress is tiered by diameter in both ISO 898-1 and SAE J429 — Class 8.8 is 580 MPa up to M16 and 600 MPa from M18 up, and SAE Grade 2 and Grade 5 each step down above a threshold diameter — and we apply the tier that belongs to each size. And the K-factor is the dominant source of real-world scatter: it is an empirical friction estimate, and actual joints routinely vary by more than the 2% figure above. For any critical joint, verify against the manufacturer’s specification or measure preload directly.
The lug nut torque and component torque pages work differently from the bolt charts, and it is worth being explicit about how.
These figures are manufacturer specifications, not calculations. A wheel joint, a spark plug seat and an aluminium oil pan are not the simple steel-on-steel joints that T = K × D × F models. The controlling limit is usually the softer component or a sealing element, so the formula would give the wrong answer. Those pages report what vehicle manufacturers publish.
They are keyed to a generation, not a single model year. Each vehicle page names the generation and year range the figure applies to, and lists earlier generations separately where the pattern, thread or torque changed. Trim levels with different wheel packages can still differ.
Verify against your own manual before relying on them. Manufacturers revise specifications, and a vehicle fitted with aftermarket wheels or replacement hardware may need a different figure entirely. Treat these pages as a fast reference and a cross-check — not as a replacement for the owner’s manual or service manual for your specific vehicle.
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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