M56 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 2030.0 mm² · Proof load: 1,177,400 N · Clamp load (75%): 883,050 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	9890.2	7294.6	87535.7	100852.3
Oiled	0.15	7417.6	5470.9	65651.3	75638.8
Zinc Plated	0.18	8901.1	6565.1	78781.4	90766.3
Waxed	0.1	4945.1	3647.3	43767.8	50426.2
MoS₂	0.12	5934.1	4376.8	52521.2	60511.2
Galvanized	0.25	12362.7	9118.3	109419.2	126064.9

Stress area: 2120.0 mm² · Proof load: 1,229,600 N · Clamp load (75%): 922,200 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	10328.6	7618.0	91415.9	105322.8
Oiled	0.15	7746.5	5713.5	68562.3	78992.6
Zinc Plated	0.18	9295.8	6856.2	82274.8	94791.1
Waxed	0.1	5164.3	3809.0	45707.9	52661.4
MoS₂	0.12	6197.2	4570.8	54849.9	63194.1
Galvanized	0.25	12910.8	9522.5	114270.3	131654.0

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 2030.0 mm² = 883,050 N

Step 2 — Torque (dry): T = 0.20 × 0.0560 m × 883,050 N = 9890.2 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.

SizeM56

Class8.8

Diameter56 mm

Pitch (coarse)5.5 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa