M4 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 8.78 mm² · Proof load: 3,863 N · Clamp load (75%): 2,897 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	2.3	1.7	20.4	23.5
Oiled	0.15	1.7	1.3	15.0	17.3
Zinc Plated	0.18	2.1	1.5	18.6	21.4
Waxed	0.1	1.2	0.9	10.6	12.2
MoS₂	0.12	1.4	1.0	12.4	14.3
Galvanized	0.25	2.9	2.1	25.7	29.6

Stress area: 9.79 mm² · Proof load: 4,308 N · Clamp load (75%): 3,231 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	2.6	1.9	23.0	26.5
Oiled	0.15	1.9	1.4	16.8	19.4
Zinc Plated	0.18	2.3	1.7	20.4	23.5
Waxed	0.1	1.3	1.0	11.5	13.3
MoS₂	0.12	1.6	1.2	14.2	16.3
Galvanized	0.25	3.2	2.4	28.3	32.6

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 8.78 mm² = 2,897 N

Step 2 — Torque (dry): T = 0.20 × 0.0040 m × 2,897 N = 2.3 N·m

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

Industrial machinery, agricultural equipment, elevated load requirements

• 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

Class6.8

Diameter4 mm

Pitch (coarse)0.7 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa