M8 Grade 9.8 Torque Specification

Torque Values by Surface Condition

Stress area: 36.61 mm² · Proof load: 23,796 N · Clamp load (75%): 17,847 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	28.6	21.1	253.1	291.6
Oiled	0.15	21.4	15.8	189.4	218.2
Zinc Plated	0.18	25.7	19.0	227.5	262.1
Waxed	0.1	14.3	10.5	126.6	145.8
MoS₂	0.12	17.1	12.6	151.3	174.4
Galvanized	0.25	35.7	26.3	316.0	364.0

Stress area: 39.17 mm² · Proof load: 25,460 N · Clamp load (75%): 19,095 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	30.6	22.6	270.8	312.0
Oiled	0.15	22.9	16.9	202.7	233.5
Zinc Plated	0.18	27.5	20.3	243.4	280.4
Waxed	0.1	15.3	11.3	135.4	156.0
MoS₂	0.12	18.3	13.5	162.0	186.6
Galvanized	0.25	38.2	28.2	338.1	389.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 650 MPa × 36.61 mm² = 17,847 N

Step 2 — Torque (dry): T = 0.20 × 0.0080 m × 17,847 N = 28.6 N·m

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

Heavy-duty automotive, high-performance machinery (limited availability, mostly M16 and smaller)

• 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

Class9.8

Diameter8 mm

Pitch (coarse)1.25 mm

Tensile900 MPa

Yield720 MPa

Proof650 MPa