🔩 Bolt Torque Reference
Every column below produces the same clamp force. They differ only in friction — which is where most of your applied torque actually goes. Class 8.8 (580 MPa proof) at 75% of proof load, computed by the same bolt torque calculator this site runs.
| Thread | Stress area | Preload | dry K = 0.2 | zinc plated K = 0.22 | lightly oiled K = 0.18 | lubricated K = 0.15 | waxed or moly K = 0.12 |
|---|---|---|---|---|---|---|---|
| M3 ×0.5 | 5.03 mm² | 2.19 kN | 1.31 0.97 lb·ft | 1.44 1.07 lb·ft | 1.18 0.87 lb·ft | 0.98 0.73 lb·ft | 0.79 0.58 lb·ft |
| M4 ×0.7 | 8.78 mm² | 3.82 kN | 3.05 2.25 lb·ft | 3.36 2.48 lb·ft | 2.75 2.03 lb·ft | 2.29 1.69 lb·ft | 1.83 1.35 lb·ft |
| M5 ×0.8 | 14.18 mm² | 6.17 kN | 6.17 4.55 lb·ft | 6.79 5.01 lb·ft | 5.55 4.1 lb·ft | 4.63 3.41 lb·ft | 3.7 2.73 lb·ft |
| M6 ×1 | 20.12 mm² | 8.75 kN | 10.5 7.75 lb·ft | 11.55 8.52 lb·ft | 9.45 6.97 lb·ft | 7.88 5.81 lb·ft | 6.3 4.65 lb·ft |
| M8 ×1.25 | 36.61 mm² | 15.92 kN | 25.48 18.79 lb·ft | 28.03 20.67 lb·ft | 22.93 16.91 lb·ft | 19.11 14.09 lb·ft | 15.29 11.28 lb·ft |
| M10 ×1.5 | 57.99 mm² | 25.23 kN | 50.45 37.21 lb·ft | 55.5 40.93 lb·ft | 45.41 33.49 lb·ft | 37.84 27.91 lb·ft | 30.27 22.33 lb·ft |
| M12 ×1.75 | 84.27 mm² | 36.66 kN | 87.97 64.89 lb·ft | 96.77 71.37 lb·ft | 79.18 58.4 lb·ft | 65.98 48.66 lb·ft | 52.78 38.93 lb·ft |
| M14 ×2 | 115.44 mm² | 50.22 kN | 140.6 103.7 lb·ft | 154.67 114.07 lb·ft | 126.54 93.33 lb·ft | 105.45 77.78 lb·ft | 84.36 62.22 lb·ft |
| M16 ×2 | 156.67 mm² | 68.15 kN | 218.08 160.85 lb·ft | 239.89 176.93 lb·ft | 196.27 144.76 lb·ft | 163.56 120.64 lb·ft | 130.85 96.51 lb·ft |
| M20 ×2.5 | 244.79 mm² | 106.49 kN | 425.94 314.16 lb·ft | 468.54 345.57 lb·ft | 383.35 282.74 lb·ft | 319.46 235.62 lb·ft | 255.56 188.49 lb·ft |
| M24 ×3 | 352.5 mm² | 153.34 kN | 736.03 542.86 lb·ft | 809.63 597.15 lb·ft | 662.42 488.58 lb·ft | 552.02 407.15 lb·ft | 441.62 325.72 lb·ft |
Reading the table
Read across, not down. Every figure in an M10 row delivers 25.23 kN of clamp force. The torque ranges from 30.27 to 55.5N·m — a factor of 1.83— because friction is consuming a different share of it in each case. That is the single most important thing this table shows.
The dangerous direction is lubrication. Apply the dry figure of 50.45N·m to a waxed M10 and you generate roughly two-thirds more preload than intended, taking a bolt aimed at 75% of proof well past it. A torque number is only meaningful alongside the condition it assumes — and if a specification does not state one, that is a question rather than a licence to guess.
The spread is the same at every size because the nut factor enters the model linearly. Small fasteners have small numbers and the same proportional sensitivity, which is worth remembering on the sizes people are least careful with.
Estimates only. This is T = K · F · dfor a single bolt in isolation. It knows nothing about joint stiffness, gaskets, relaxation after tightening, reuse, or tightening sequence on a multi-bolt joint. Anything structural or safety-critical — wheels, brakes, steering, suspension, lifting equipment, pressure containment — takes its figures from the manufacturer or the designing engineer. See what a torque wrench cannot tell you.
❓ Frequently Asked Questions
Why does one bolt have five different torque figures?
Because torque is mostly spent on friction, not on stretching the bolt. All five columns produce the SAME clamp force — 25.23 kN for an M10 — and differ only in the nut factor, which lumps the friction into one number. The spread is about 1.83× from the most to the least frictional condition.
What happens if I use a dry figure on a lubricated bolt?
You overshoot the preload badly. An M10 wants 50.45 N·m dry and 30.27 N·m waxed for the same clamp force. Apply the dry figure to a waxed fastener and the preload generated is roughly two-thirds higher than intended — taking a bolt targeted at 75% of proof well past it. A torque spec without its assumed condition is incomplete.
Why is class 8.8 shown at 580 MPa and not 640?
580 MPa is the proof strength of property class 8.8 under ISO 898-1; 640 MPa is its yield strength. Preload targets are set as a fraction of proof load, so using the yield figure inflates every derived number by about 10%. The class markings encode the tensile strength and the yield-to-tensile ratio, not the proof strength directly, which is why the confusion is common.
Can I use these figures on my car or on anything structural?
No. These are educational estimates from a general model for a single bolt in isolation. Wheels, brakes, steering, suspension, lifting equipment, pressure containment and anything structural take their figures from the manufacturer or the designing engineer — along with the tightening sequence, the assumed condition, and any re-check interval, none of which a general model knows about.