M36×3 Torque Spec
Calculated preload torque by grade, plus what actually changes the number.
M36×3 · 8.8 · dry threads
2709 N·m
1998 lb-ft · targets 376.2
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 | 1051 | 788 | 775 | 146 kN | 346 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 2709 | 2032 | 1998 | 376.2 kN | 692 kN |
| 10.9 Alloy steel, Q&T — high strength | 3877 | 2907 | 2859 | 538.4 kN | 899.5 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 4531 | 3398 | 3342 | 629.2 kN | 1055.2 kN |
| A2-70 304 stainless, cold worked | 2102 | 1576 | 1550 | 291.9 kN | 605.5 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 M36×3 8.8 fastener under different conditions:
| Thread condition | Nut factor K | Torque for same preload |
|---|---|---|
| Plain / as-received, dry | 0.20 | 2709 N·m |
| Zinc plated, dry | 0.22 | 2980 N·m |
| Black oxide, lightly oiled | 0.18 | 2438 N·m |
| Machine oil on threads | 0.15 | 2032 N·m |
| Molybdenum disulfide / anti-seize | 0.12 | 1625 N·m |
| Waxed or PTFE coated | 0.10 | 1354 N·m |
Torquing a lubricated bolt to the dry spec overloads it — the
1354
N·m row and the
2709
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 (864.94 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.