M6 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 20.12 mm² · Proof load: 11,670 N · Clamp load (75%): 8,752 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	10.5	7.7	92.9	107.1
Oiled	0.15	7.9	5.8	69.9	80.6
Zinc Plated	0.18	9.5	7.0	84.1	96.9
Waxed	0.1	5.3	3.9	46.9	54.0
MoS₂	0.12	6.3	4.6	55.8	64.2
Galvanized	0.25	13.1	9.7	115.9	133.6

Stress area: 22.03 mm² · Proof load: 12,777 N · Clamp load (75%): 9,583 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	11.5	8.5	101.8	117.3
Oiled	0.15	8.6	6.3	76.1	87.7
Zinc Plated	0.18	10.3	7.6	91.2	105.0
Waxed	0.1	5.7	4.2	50.4	58.1
MoS₂	0.12	6.9	5.1	61.1	70.4
Galvanized	0.25	14.4	10.6	127.5	146.8

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 20.12 mm² = 8,752 N

Step 2 — Torque (dry): T = 0.20 × 0.0060 m × 8,752 N = 10.5 N·m

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

Automotive engines, structural connections, high-strength machinery, flanged joints — the most common high-strength 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.

SizeM6

Class8.8

Diameter6 mm

Pitch (coarse)1.0 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa