M56 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 2030.0 mm² · Proof load: 893,200 N · Clamp load (75%): 669,900 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	7502.9	5533.9	66406.3	76508.6
Oiled	0.15	5627.2	4150.4	49804.9	57381.7
Zinc Plated	0.18	6752.6	4980.5	59765.6	68857.6
Waxed	0.1	3751.4	2766.9	33202.7	38253.8
MoS₂	0.12	4501.7	3320.3	39843.4	45904.7
Galvanized	0.25	9378.6	6917.3	83007.6	95635.5

Stress area: 2120.0 mm² · Proof load: 932,800 N · Clamp load (75%): 699,600 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	7835.5	5779.2	69350.1	79900.2
Oiled	0.15	5876.6	4334.4	52012.3	59924.9
Zinc Plated	0.18	7052.0	5201.3	62415.5	71910.7
Waxed	0.1	3917.8	2889.6	34675.5	39950.6
MoS₂	0.12	4701.3	3467.5	41610.0	47940.1
Galvanized	0.25	9794.4	7224.0	86687.8	99875.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 2030.0 mm² = 669,900 N

Step 2 — Torque (dry): T = 0.20 × 0.0560 m × 669,900 N = 7502.9 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.

SizeM56

Class6.8

Diameter56 mm

Pitch (coarse)5.5 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa