M20 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 244.79 mm² · Proof load: 107,708 N · Clamp load (75%): 80,781 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	323.1	238.3	2859.7	3294.7
Oiled	0.15	242.3	178.7	2144.5	2470.8
Zinc Plated	0.18	290.8	214.5	2573.8	2965.3
Waxed	0.1	161.6	119.2	1430.3	1647.9
MoS₂	0.12	193.9	143.0	1716.2	1977.2
Galvanized	0.25	403.9	297.9	3574.8	4118.6

Stress area: 271.5 mm² · Proof load: 119,460 N · Clamp load (75%): 89,595 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	358.4	264.3	3172.1	3654.7
Oiled	0.15	268.8	198.3	2379.1	2741.0
Zinc Plated	0.18	322.5	237.9	2854.4	3288.6
Waxed	0.1	179.2	132.2	1586.1	1827.3
MoS₂	0.12	215.0	158.6	1902.9	2192.4
Galvanized	0.25	448.0	330.4	3965.1	4568.3

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 244.79 mm² = 80,781 N

Step 2 — Torque (dry): T = 0.20 × 0.0200 m × 80,781 N = 323.1 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.

SizeM20

Class6.8

Diameter20 mm

Pitch (coarse)2.5 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa