M42 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 1120.9 mm² · Proof load: 650,122 N · Clamp load (75%): 487,592 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	4095.8	3020.9	36250.9	41765.7
Oiled	0.15	3071.8	2265.6	27187.7	31323.8
Zinc Plated	0.18	3686.2	2718.8	32625.6	37588.9
Waxed	0.1	2047.9	1510.5	18125.5	20882.8
MoS₂	0.12	2457.5	1812.6	21750.7	25059.6
Galvanized	0.25	5119.7	3776.1	45313.2	52206.6

Stress area: 1205.7 mm² · Proof load: 699,306 N · Clamp load (75%): 524,480 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	4405.6	3249.4	38992.9	44924.8
Oiled	0.15	3304.2	2437.1	29244.6	33693.6
Zinc Plated	0.18	3965.1	2924.5	35094.1	40432.9
Waxed	0.1	2202.8	1624.7	19496.4	22462.4
MoS₂	0.12	2643.4	1949.7	23396.1	26955.3
Galvanized	0.25	5507.0	4061.8	48741.1	56156.0

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 1120.9 mm² = 487,592 N

Step 2 — Torque (dry): T = 0.20 × 0.0420 m × 487,592 N = 4095.8 N·m

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

Automotive engines, structural connections, high-strength machinery, flanged joints — the most common high-strength 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.

SizeM42

Class8.8

Diameter42 mm

Pitch (coarse)4.5 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa