M39 Grade 12.9 Torque Specification

Torque Values by Surface Condition

Stress area: 976.0 mm² · Proof load: 946,720 N · Clamp load (75%): 710,040 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	5538.3	4084.8	49018.1	56475.2
Oiled	0.15	4153.7	3063.6	36763.4	42356.1
Zinc Plated	0.18	4984.5	3676.4	44116.6	50827.9
Waxed	0.1	2769.2	2042.5	24509.5	28238.1
MoS₂	0.12	3323.0	2450.9	29411.0	33885.3
Galvanized	0.25	6922.9	5106.1	61272.9	70594.2

Stress area: 1028.4 mm² · Proof load: 997,548 N · Clamp load (75%): 748,161 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	5835.7	4304.2	51650.3	59507.8
Oiled	0.15	4376.7	3228.1	38737.1	44630.1
Zinc Plated	0.18	5252.1	3873.7	46485.0	53556.7
Waxed	0.1	2917.8	2152.1	25824.7	29753.4
MoS₂	0.12	3501.4	2582.5	30990.0	35704.5
Galvanized	0.25	7294.6	5380.2	64562.7	74384.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 970 MPa × 976.0 mm² = 710,040 N

Step 2 — Torque (dry): T = 0.20 × 0.0390 m × 710,040 N = 5538.3 N·m

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

Socket head cap screws, racing/motorsport, aerospace, maximum strength applications — highest standard 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.

SizeM39

Class12.9

Diameter39 mm

Pitch (coarse)4.0 mm

Tensile1220 MPa

Yield1100 MPa

Proof970 MPa