M52×5 Torque Spec
Calculated preload torque by grade, plus what actually changes the number.
M52×5 · 8.8 · dry threads
7952 N·m
5865 lb-ft · targets 764.7
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 | 3085 | 2314 | 2275 | 296.6 kN | 703.1 kN |
| 8.8 Medium-carbon, quenched & tempered — the default structural grade | 7952 | 5964 | 5865 | 764.7 kN | 1406.3 kN |
| 10.9 Alloy steel, Q&T — high strength | 11380 | 8535 | 8394 | 1094.3 kN | 1828.1 kN |
| 12.9 Alloy steel, Q&T — highest common grade (socket head cap screws) | 13300 | 9975 | 9809 | 1278.8 kN | 2144.6 kN |
| A2-70 304 stainless, cold worked | 6170 | 4628 | 4551 | 593.3 kN | 1230.5 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 M52×5 8.8 fastener under different conditions:
| Thread condition | Nut factor K | Torque for same preload |
|---|---|---|
| Plain / as-received, dry | 0.20 | 7952 N·m |
| Zinc plated, dry | 0.22 | 8748 N·m |
| Black oxide, lightly oiled | 0.18 | 7157 N·m |
| Machine oil on threads | 0.15 | 5964 N·m |
| Molybdenum disulfide / anti-seize | 0.12 | 4771 N·m |
| Waxed or PTFE coated | 0.10 | 3976 N·m |
Torquing a lubricated bolt to the dry spec overloads it — the
3976
N·m row and the
7952
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 (1757.84 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.