M8 Grade 10.9 Torque Specification

Torque Values by Surface Condition

Stress area: 36.61 mm² · Proof load: 30,386 N · Clamp load (75%): 22,790 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	36.5	26.9	323.1	372.2
Oiled	0.15	27.3	20.1	241.6	278.4
Zinc Plated	0.18	32.8	24.2	290.3	334.5
Waxed	0.1	18.2	13.4	161.1	185.6
MoS₂	0.12	21.9	16.2	193.8	223.3
Galvanized	0.25	45.6	33.6	403.6	465.0

Stress area: 39.17 mm² · Proof load: 32,511 N · Clamp load (75%): 24,383 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	39.0	28.8	345.2	397.7
Oiled	0.15	29.3	21.6	259.3	298.8
Zinc Plated	0.18	35.1	25.9	310.7	357.9
Waxed	0.1	19.5	14.4	172.6	198.8
MoS₂	0.12	23.4	17.3	207.1	238.6
Galvanized	0.25	48.8	36.0	431.9	497.6

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 830 MPa × 36.61 mm² = 22,790 N

Step 2 — Torque (dry): T = 0.20 × 0.0080 m × 22,790 N = 36.5 N·m

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

Structural steel (equivalent to ASTM A490), heavy machinery, high-strength critical joints, pressure vessels

• 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

Class10.9

Diameter8 mm

Pitch (coarse)1.25 mm

Tensile1040 MPa

Yield940 MPa

Proof830 MPa