Bolt Torque Calculator
Tightening torque for M3-M36 bolts in grades 8.8, 10.9, and 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. Use 50% for reused bolts or uncertain condition. Use 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 — never guess.
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 the dry-torque value with lubricated threads, you'll 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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