M8 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 36.61 mm² · Proof load: 16,108 N · Clamp load (75%): 12,081 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	19.3	14.2	170.8	196.8
Oiled	0.15	14.5	10.7	128.3	147.9
Zinc Plated	0.18	17.4	12.8	154.0	177.4
Waxed	0.1	9.7	7.2	85.9	98.9
MoS₂	0.12	11.6	8.6	102.7	118.3
Galvanized	0.25	24.2	17.8	214.2	246.8

Stress area: 39.17 mm² · Proof load: 17,235 N · Clamp load (75%): 12,926 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	20.7	15.3	183.2	211.1
Oiled	0.15	15.5	11.4	137.2	158.1
Zinc Plated	0.18	18.6	13.7	164.6	189.7
Waxed	0.1	10.3	7.6	91.2	105.0
MoS₂	0.12	12.4	9.1	109.7	126.4
Galvanized	0.25	25.9	19.1	229.2	264.1

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 36.61 mm² = 12,081 N

Step 2 — Torque (dry): T = 0.20 × 0.0080 m × 12,081 N = 19.3 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.

SizeM8

Class6.8

Diameter8 mm

Pitch (coarse)1.25 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa