M64 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 2676.0 mm² · Proof load: 1,177,440 N · Clamp load (75%): 883,080 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	11303.4	8337.0	100043.6	115263.0
Oiled	0.15	8477.6	6252.8	75033.1	86447.8
Zinc Plated	0.18	10173.1	7503.3	90039.6	103737.1
Waxed	0.1	5651.7	4168.5	50021.8	57631.5
MoS₂	0.12	6782.1	5002.2	60026.7	69158.4
Galvanized	0.25	14129.3	10421.2	125054.9	144079.3

Stress area: 2809.0 mm² · Proof load: 1,235,960 N · Clamp load (75%): 926,970 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	11865.2	8751.3	105015.9	120991.8
Oiled	0.15	8898.9	6563.5	78761.9	90743.9
Zinc Plated	0.18	10678.7	7876.2	94514.5	108892.8
Waxed	0.1	5932.6	4375.7	52508.0	60495.9
MoS₂	0.12	7119.1	5250.8	63009.4	72594.9
Galvanized	0.25	14831.5	10939.2	131269.9	151239.8

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 2676.0 mm² = 883,080 N

Step 2 — Torque (dry): T = 0.20 × 0.0640 m × 883,080 N = 11303.4 N·m

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

Industrial machinery, agricultural equipment, elevated load requirements

• 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

Class6.8

Diameter64 mm

Pitch (coarse)6.0 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa