M8 Grade 12.9 Torque Specification

Torque Values by Surface Condition

Stress area: 36.61 mm² · Proof load: 35,512 N · Clamp load (75%): 26,634 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	42.6	31.4	377.0	434.4
Oiled	0.15	32.0	23.6	283.2	326.3
Zinc Plated	0.18	38.4	28.3	339.9	391.6
Waxed	0.1	21.3	15.7	188.5	217.2
MoS₂	0.12	25.6	18.9	226.6	261.0
Galvanized	0.25	53.3	39.3	471.7	543.5

Stress area: 39.17 mm² · Proof load: 37,995 N · Clamp load (75%): 28,496 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	45.6	33.6	403.6	465.0
Oiled	0.15	34.2	25.2	302.7	348.7
Zinc Plated	0.18	41.0	30.2	362.9	418.1
Waxed	0.1	22.8	16.8	201.8	232.5
MoS₂	0.12	27.4	20.2	242.5	279.4
Galvanized	0.25	57.0	42.0	504.5	581.2

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 970 MPa × 36.61 mm² = 26,634 N

Step 2 — Torque (dry): T = 0.20 × 0.0080 m × 26,634 N = 42.6 N·m

Proof stress per ISO 898-1:2013 Table 4. Stress area per ISO 898-1 Annex A. K-factor per VDI 2230.

Socket head cap screws, racing/motorsport, aerospace, maximum strength applications — highest standard grade

• Torque values are for standard hex bolts with ISO metric threads. Socket head cap screws may have different requirements.
• Lubrication reduces required torque significantly — using dry torque values on lubricated bolts risks exceeding yield strength.
• For critical or safety-related applications, always consult the manufacturer's specifications or applicable design standard (e.g., VDI 2230).
• Re-used bolts may have altered friction characteristics. Inspect threads before reuse.

SizeM8

Class12.9

Diameter8 mm

Pitch (coarse)1.25 mm

Tensile1220 MPa

Yield1100 MPa

Proof970 MPa