M42 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 1120.9 mm² · Proof load: 493,196 N · Clamp load (75%): 369,897 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	3107.1	2291.7	27500.2	31683.7
Oiled	0.15	2330.4	1718.8	20625.8	23763.6
Zinc Plated	0.18	2796.4	2062.5	24750.2	28515.5
Waxed	0.1	1553.6	1145.9	13750.5	15842.4
MoS₂	0.12	1864.3	1375.0	16500.5	19010.6
Galvanized	0.25	3883.9	2864.6	34375.4	39604.9

Stress area: 1205.7 mm² · Proof load: 530,508 N · Clamp load (75%): 397,881 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	3342.2	2465.1	29581.0	34081.1
Oiled	0.15	2506.7	1848.8	22186.2	25561.3
Zinc Plated	0.18	3008.0	2218.6	26623.1	30673.2
Waxed	0.1	1671.1	1232.5	14790.5	17040.5
MoS₂	0.12	2005.3	1479.0	17748.4	20448.4
Galvanized	0.25	4177.8	3081.4	36976.7	42601.9

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 1120.9 mm² = 369,897 N

Step 2 — Torque (dry): T = 0.20 × 0.0420 m × 369,897 N = 3107.1 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.

SizeM42

Class6.8

Diameter42 mm

Pitch (coarse)4.5 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa