M4 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 8.78 mm² · Proof load: 5,092 N · Clamp load (75%): 3,819 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	3.1	2.3	27.4	31.6
Oiled	0.15	2.3	1.7	20.4	23.5
Zinc Plated	0.18	2.7	2.0	23.9	27.5
Waxed	0.1	1.5	1.1	13.3	15.3
MoS₂	0.12	1.8	1.3	15.9	18.4
Galvanized	0.25	3.8	2.8	33.6	38.7

Stress area: 9.79 mm² · Proof load: 5,678 N · Clamp load (75%): 4,259 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	3.4	2.5	30.1	34.7
Oiled	0.15	2.6	1.9	23.0	26.5
Zinc Plated	0.18	3.1	2.3	27.4	31.6
Waxed	0.1	1.7	1.3	15.0	17.3
MoS₂	0.12	2.0	1.5	17.7	20.4
Galvanized	0.25	4.3	3.2	38.1	43.8

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 8.78 mm² = 3,819 N

Step 2 — Torque (dry): T = 0.20 × 0.0040 m × 3,819 N = 3.1 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.

SizeM4

Class8.8

Diameter4 mm

Pitch (coarse)0.7 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa