M33 Grade 12.9 Torque Specification

Torque Values by Surface Condition

Stress area: 693.55 mm² · Proof load: 672,744 N · Clamp load (75%): 504,558 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	3330.1	2456.2	29473.9	33957.7
Oiled	0.15	2497.6	1842.1	22105.6	25468.5
Zinc Plated	0.18	2997.1	2210.5	26526.6	30562.0
Waxed	0.1	1665.0	1228.0	14736.5	16978.3
MoS₂	0.12	1998.0	1473.6	17683.8	20374.0
Galvanized	0.25	4162.6	3070.2	36842.1	42446.9

Stress area: 760.85 mm² · Proof load: 738,024 N · Clamp load (75%): 553,518 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	3653.2	2694.5	32333.6	37252.4
Oiled	0.15	2739.9	2020.8	24250.2	27939.3
Zinc Plated	0.18	3287.9	2425.0	29100.4	33527.4
Waxed	0.1	1826.6	1347.2	16166.8	18626.2
MoS₂	0.12	2191.9	1616.7	19400.0	22351.2
Galvanized	0.25	4566.5	3368.1	40416.9	46565.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 970 MPa × 693.55 mm² = 504,558 N

Step 2 — Torque (dry): T = 0.20 × 0.0330 m × 504,558 N = 3330.1 N·m

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

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.

SizeM33

Class12.9

Diameter33 mm

Pitch (coarse)3.5 mm

Tensile1220 MPa

Yield1100 MPa

Proof970 MPa