Bolt Torque Calculator
Tightening torque for M3–M36 bolts in grades 8.8, 10.9, 12.9
M3 से M36 तक बोल्ट का torque — Grade 8.8, 10.9, 12.9 के लिए
Bolt tightening torque is the twisting force applied with a torque wrench to tension a bolt into its clamped joint. The correct torque depends on three variables: bolt size (M-number), bolt grade (8.8, 10.9, or 12.9), and thread friction (dry, lightly oiled, or lubricated). The standard formula is T = K × F × d, where T is torque, K is the friction coefficient (typically 0.2 dry, 0.16 oiled, 0.12 with anti-seize), F is the target preload (usually 70% of proof load), and d is the nominal bolt diameter. A common M10 Grade 8.8 bolt tightens dry to about 48 Nm, lightly oiled to 38 Nm, and with anti-seize paste to 28 Nm. Unbrako socket head cap screws are typically Grade 12.9 — capable of handling roughly 40% more torque than the same Grade 8.8 equivalent. Always use a calibrated torque wrench.
Calculator
M10 × pitch 1.5 mm — tensile stress area 58 mm²
Use 70% for most applications. 50% for reused bolts or uncertain condition. 90% only for precision-controlled assemblies.
= 34.7 ft·lb. Formula: T = K × F × d → 0.2 × 23.5 kN × 0.010 m. Always use a calibrated click-type torque wrench.
ƒFormula
T = K × F × d where F = 0.70 × σ_p × A_sT is tightening torque (Nm). K is nut factor: 0.20 dry, 0.16 lightly oiled, 0.12 with lubricant / anti-seize. F is target preload force, usually 70% of bolt proof load. σ_p is proof stress (580 MPa for grade 8.8, 830 for 10.9, 970 for 12.9). A_s is the tensile stress area of the thread. d is the nominal bolt diameter in metres.
Units: Torque: Newton-metre (Nm) · kilogram-force metre (kgf·m) · Diameter: mm
Bolt ko kitna tight karein? (Torque kya hai?)
Har bolt ki ek sahi tightening torque hoti hai — na usse kam, na zyada. Kam torque lagane se joint slip ho sakta hai; zyada torque bolt ko stretch kar ke tod deta hai. Torque = K × F × d formula ka matlab — K friction coefficient (dry joints ke liye 0.2, oiled ke liye 0.16), F preload force jo bolt ko tension mein rakhta hai (proof load ka 70%), aur d bolt ka diameter. Unbrako brand ke socket head cap screws aam taur pe Grade 12.9 hote hain — inka tensile strength 1220 MPa hota hai, aur yeh Grade 8.8 bolts se 40% zyada torque le sakte hain. Hamesha calibrated torque wrench use karein, aandaaz se tight mat karein.
Worked Examples
Tightening an M10 engine mount bolt
Problem: You need to tighten an M10 Grade 8.8 engine mount bolt on a mildly oiled thread.
Solution: M10 × 8.8 × lightly oiled (K=0.16). A_s for M10 = 58 mm². Preload F = 0.7 × 580 × 58 = 23,548 N. T = 0.16 × 23,548 × 0.010 = 37.7 Nm ≈ 38 Nm. Use a 38 Nm click torque wrench.
Unbrako M12 cap screw for die clamping
Problem: A die needs four M12 Unbrako Grade 12.9 socket head cap screws, assembled dry.
Solution: M12 × 12.9 × dry (K=0.2). A_s for M12 = 84.3 mm². Preload F = 0.7 × 970 × 84.3 = 57,240 N. T = 0.2 × 57,240 × 0.012 = 137 Nm. Use a 1/2-inch drive torque wrench set to 137 Nm.
Why is anti-seize paste torque always lower?
Problem: An M16 Grade 10.9 dry torque is 210 Nm but with anti-seize only 150 Nm. Why?
Solution: Anti-seize reduces thread friction — less of the applied torque is lost to friction, so more of it becomes preload. If you apply dry-torque value with lubricated threads, you will over-tension and break the bolt. Always match torque to thread condition.
Bolt Tightening Torque (Nm) — Grades 8.8, 10.9, 12.9 — Dry Thread
Bolt torque चार्ट (Nm) — Grade 8.8, 10.9, 12.9 — dry thread
| Size | Pitch (mm) | 8.8 (Nm) | 10.9 (Nm) | 12.9 (Nm) |
|---|---|---|---|---|
| M4 | 0.7 | 3.0 | 4.4 | 5.1 |
| M5 | 0.8 | 5.9 | 8.7 | 10.2 |
| M6 | 1.0 | 10.1 | 14.9 | 17.4 |
| M8 | 1.25 | 24.6 | 36.1 | 42.2 |
| M10 | 1.5 | 48.0 | 71.0 | 83.0 |
| M12 | 1.75 | 83.0 | 122.0 | 143.0 |
| M14 | 2.0 | 132.0 | 194.0 | 227.0 |
| M16 | 2.0 | 205.0 | 302.0 | 354.0 |
| M18 | 2.5 | 283.0 | 415.0 | 486.0 |
| M20 | 2.5 | 400.0 | 587.0 | 688.0 |
| M22 | 2.5 | 544.0 | 798.0 | 935.0 |
| M24 | 3.0 | 691.0 | 1014.0 | 1187.0 |
| M27 | 3.0 | 1010.0 | 1482.0 | 1735.0 |
| M30 | 3.5 | 1372.0 | 2013.0 | 2357.0 |
Dry thread values (K=0.20). Multiply by 0.80 for lightly oiled, 0.60 for anti-seize / lubricated threads. 1 kgf·m ≈ 9.807 Nm.
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Unbrako Socket Head Cap Screws
Grade 12.9 metric cap screws, M3 to M36. Genuine, with proper batch marking.
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