M64 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 2676.0 mm² · Proof load: 1,552,080 N · Clamp load (75%): 1,164,060 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	14900.0	10989.7	131876.2	151938.3
Oiled	0.15	11175.0	8242.3	98907.1	113953.7
Zinc Plated	0.18	13410.0	9890.7	118688.6	136744.5
Waxed	0.1	7450.0	5494.8	65938.1	75969.1
MoS₂	0.12	8940.0	6593.8	79125.7	91163.0
Galvanized	0.25	18625.0	13737.1	164845.2	189922.9

Stress area: 2809.0 mm² · Proof load: 1,629,220 N · Clamp load (75%): 1,221,915 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	15640.5	11535.8	138430.2	159489.3
Oiled	0.15	11730.4	8651.9	103822.8	119617.2
Zinc Plated	0.18	14076.5	10382.3	124587.6	143540.9
Waxed	0.1	7820.3	5768.0	69215.5	79745.2
MoS₂	0.12	9384.3	6921.5	83058.1	95693.6
Galvanized	0.25	19550.6	14419.8	173037.5	199361.4

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 2676.0 mm² = 1,164,060 N

Step 2 — Torque (dry): T = 0.20 × 0.0640 m × 1,164,060 N = 14900.0 N·m

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

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.

SizeM64

Class8.8

Diameter64 mm

Pitch (coarse)6.0 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa