M8 Grade 5.8 Torque Specification

Torque Values by Surface Condition

Stress area: 36.61 mm² · Proof load: 13,912 N · Clamp load (75%): 10,434 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	16.7	12.3	147.8	170.3
Oiled	0.15	12.5	9.2	110.6	127.5
Zinc Plated	0.18	15.0	11.1	132.8	153.0
Waxed	0.1	8.3	6.1	73.5	84.6
MoS₂	0.12	10.0	7.4	88.5	102.0
Galvanized	0.25	20.9	15.4	185.0	213.1

Stress area: 39.17 mm² · Proof load: 14,885 N · Clamp load (75%): 11,163 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	17.9	13.2	158.4	182.5
Oiled	0.15	13.4	9.9	118.6	136.6
Zinc Plated	0.18	16.1	11.9	142.5	164.2
Waxed	0.1	8.9	6.6	78.8	90.8
MoS₂	0.12	10.7	7.9	94.7	109.1
Galvanized	0.25	22.3	16.4	197.4	227.4

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 380 MPa × 36.61 mm² = 10,434 N

Step 2 — Torque (dry): T = 0.20 × 0.0080 m × 10,434 N = 16.7 N·m

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

General industrial fastening, equipment mounting, moderate structural loads

• 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

Class5.8

Diameter8 mm

Pitch (coarse)1.25 mm

Tensile520 MPa

Yield420 MPa

Proof380 MPa