M18 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 192.47 mm² · Proof load: 84,687 N · Clamp load (75%): 63,515 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	228.7	168.7	2024.2	2332.1
Oiled	0.15	171.5	126.5	1517.9	1748.8
Zinc Plated	0.18	205.8	151.8	1821.5	2098.6
Waxed	0.1	114.3	84.3	1011.6	1165.5
MoS₂	0.12	137.2	101.2	1214.3	1399.1
Galvanized	0.25	285.8	210.8	2529.5	2914.4

Stress area: 216.23 mm² · Proof load: 95,141 N · Clamp load (75%): 71,356 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	256.9	189.5	2273.8	2619.7
Oiled	0.15	192.7	142.1	1705.5	1965.0
Zinc Plated	0.18	231.2	170.5	2046.3	2357.6
Waxed	0.1	128.4	94.7	1136.4	1309.3
MoS₂	0.12	154.1	113.7	1363.9	1571.4
Galvanized	0.25	321.1	236.8	2842.0	3274.3

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 192.47 mm² = 63,515 N

Step 2 — Torque (dry): T = 0.20 × 0.0180 m × 63,515 N = 228.7 N·m

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

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.

SizeM18

Class6.8

Diameter18 mm

Pitch (coarse)2.5 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa