M8 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 36.61 mm² · Proof load: 21,234 N · Clamp load (75%): 15,925 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	25.5	18.8	225.7	260.0
Oiled	0.15	19.1	14.1	169.0	194.8
Zinc Plated	0.18	22.9	16.9	202.7	233.5
Waxed	0.1	12.7	9.4	112.4	129.5
MoS₂	0.12	15.3	11.3	135.4	156.0
Galvanized	0.25	31.9	23.5	282.3	325.3

Stress area: 39.17 mm² · Proof load: 22,719 N · Clamp load (75%): 17,039 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	27.3	20.1	241.6	278.4
Oiled	0.15	20.4	15.0	180.6	208.0
Zinc Plated	0.18	24.5	18.1	216.8	249.8
Waxed	0.1	13.6	10.0	120.4	138.7
MoS₂	0.12	16.4	12.1	145.2	167.2
Galvanized	0.25	34.1	25.2	301.8	347.7

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 36.61 mm² = 15,925 N

Step 2 — Torque (dry): T = 0.20 × 0.0080 m × 15,925 N = 25.5 N·m

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

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.

SizeM8

Class8.8

Diameter8 mm

Pitch (coarse)1.25 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa