M56×4 Torque Spec
Calculated preload torque by grade, plus what actually changes the number.
M56×4 · 8.8 · dry threads
10445 N·m
7704 lb-ft · targets 932.6
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 | 4052 | 3039 | 2989 | 361.8 kN | 857.6 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 10445 | 7834 | 7704 | 932.6 kN | 1715.2 kN |
| 10.9 Alloy steel, Q&T — high strength | 14948 | 11211 | 11025 | 1334.6 kN | 2229.7 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 17469 | 13102 | 12884 | 1559.7 kN | 2615.6 kN |
| A2-70 304 stainless, cold worked | 8104 | 6078 | 5977 | 723.6 kN | 1500.8 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 M56×4 8.8 fastener under different conditions:
| Thread condition | Nut factor K | Torque for same preload |
|---|---|---|
| Plain / as-received, dry | 0.20 | 10445 N·m |
| Zinc plated, dry | 0.22 | 11490 N·m |
| Black oxide, lightly oiled | 0.18 | 9401 N·m |
| Machine oil on threads | 0.15 | 7834 N·m |
| Molybdenum disulfide / anti-seize | 0.12 | 6267 N·m |
| Waxed or PTFE coated | 0.10 | 5223 N·m |
Torquing a lubricated bolt to the dry spec overloads it — the
5223
N·m row and the
10445
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 (2143.96 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.