M39 Grade 10.9 Torque Specification

Torque Values by Surface Condition

Stress area: 976.0 mm² · Proof load: 810,080 N · Clamp load (75%): 607,560 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	4739.0	3495.3	41943.7	48324.5
Oiled	0.15	3554.2	2621.4	31457.3	36242.9
Zinc Plated	0.18	4265.1	3145.8	37749.3	43492.1
Waxed	0.1	2369.5	1747.7	20971.9	24162.3
MoS₂	0.12	2843.4	2097.2	25166.2	28994.7
Galvanized	0.25	5923.7	4369.1	52429.2	60405.2

Stress area: 1028.4 mm² · Proof load: 853,572 N · Clamp load (75%): 640,179 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	4993.4	3682.9	44195.3	50918.7
Oiled	0.15	3745.0	2762.2	33146.1	38188.5
Zinc Plated	0.18	4494.1	3314.7	39776.2	45827.2
Waxed	0.1	2496.7	1841.5	22097.7	25459.3
MoS₂	0.12	2996.0	2209.7	26516.8	30550.8
Galvanized	0.25	6241.7	4603.6	55243.7	63647.9

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 830 MPa × 976.0 mm² = 607,560 N

Step 2 — Torque (dry): T = 0.20 × 0.0390 m × 607,560 N = 4739.0 N·m

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

Structural steel (equivalent to ASTM A490), heavy machinery, high-strength critical joints, pressure vessels

• 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.

SizeM39

Class10.9

Diameter39 mm

Pitch (coarse)4.0 mm

Tensile1040 MPa

Yield940 MPa

Proof830 MPa