M18 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 192.47 mm² · Proof load: 111,633 N · Clamp load (75%): 83,724 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	301.4	222.3	2667.6	3073.4
Oiled	0.15	226.1	166.8	2001.2	2305.6
Zinc Plated	0.18	271.3	200.1	2401.2	2766.5
Waxed	0.1	150.7	111.2	1333.8	1536.7
MoS₂	0.12	180.8	133.4	1600.2	1843.7
Galvanized	0.25	376.8	277.9	3335.0	3842.3

Stress area: 216.23 mm² · Proof load: 125,413 N · Clamp load (75%): 94,060 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	338.6	249.7	2996.9	3452.8
Oiled	0.15	254.0	187.3	2248.1	2590.1
Zinc Plated	0.18	304.8	224.8	2697.7	3108.1
Waxed	0.1	169.3	124.9	1498.4	1726.4
MoS₂	0.12	203.2	149.9	1798.5	2072.1
Galvanized	0.25	423.3	312.2	3746.5	4316.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 192.47 mm² = 83,724 N

Step 2 — Torque (dry): T = 0.20 × 0.0180 m × 83,724 N = 301.4 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.

SizeM18

Class8.8

Diameter18 mm

Pitch (coarse)2.5 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa