M3.5×0.6 Torque Spec
Calculated preload torque by grade, plus what actually changes the number.
M3.5×0.6 · 8.8 · dry threads
2.06 N·m
1.52 lb-ft · targets 2.9
kN clamp load (75% of proof)
By grade
| Grade | Dry (N·m) | Lubed (N·m) | Dry (lb-ft) | Clamp load | Ultimate tensile |
|---|---|---|---|---|---|
| 4.6 Low-carbon steel, general purpose | 0.8 | 0.6 | 0.59 | 1.1 kN | 2.7 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 2.06 | 1.55 | 1.52 | 2.9 kN | 5.4 kN |
| 10.9 Alloy steel, Q&T — high strength | 2.95 | 2.21 | 2.18 | 4.2 kN | 7 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 3.45 | 2.59 | 2.54 | 4.9 kN | 8.3 kN |
| A2-70 304 stainless, cold worked | 1.6 | 1.2 | 1.18 | 2.3 kN | 4.7 kN |
Why lubrication changes everything
Roughly 90% of the torque you apply is consumed by friction — under the head and in the threads. Only about 10% becomes useful bolt stretch. That means the friction coefficient, not the bolt, sets the relationship between torque and clamp load. Here is the same M3.5×0.6 8.8 fastener under different conditions:
| Thread condition | Nut factor K | Torque for same preload |
|---|---|---|
| Plain / as-received, dry | 0.20 | 2.06 N·m |
| Zinc plated, dry | 0.22 | 2.27 N·m |
| Black oxide, lightly oiled | 0.18 | 1.86 N·m |
| Machine oil on threads | 0.15 | 1.55 N·m |
| Molybdenum disulfide / anti-seize | 0.12 | 1.24 N·m |
| Waxed or PTFE coated | 0.10 | 1.03 N·m |
Torquing a lubricated bolt to the dry spec overloads it — the
1.03
N·m row and the
2.06
N·m row produce the same clamp load. Apply the dry
number to a waxed fastener and you are at roughly twice the intended preload, which
for a 8.8 is past yield.
Assumptions behind these numbers
T = K × D × F with K = 0.20, F = 0.75 × proof load, and proof load = tensile stress area (6.78 mm²) × the grade's proof strength. This is a general-engineering starting point for a reusable steel-on-steel joint. It is not a substitute for a manufacturer's torque sequence on an engine, a suspension component, a pressure vessel or any structural connection.