M52 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 1757.73 mm² · Proof load: 773,401 N · Clamp load (75%): 580,051 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	6032.5	4449.3	53392.1	61514.6
Oiled	0.15	4524.4	3337.0	40044.3	46136.2
Zinc Plated	0.18	5429.3	4004.4	48053.4	55363.7
Waxed	0.1	3016.3	2224.7	26696.5	30757.8
MoS₂	0.12	3619.5	2669.6	32035.3	36908.8
Galvanized	0.25	7540.7	5561.7	66740.9	76894.0

Stress area: 1828.6 mm² · Proof load: 804,584 N · Clamp load (75%): 603,438 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	6275.8	4628.8	55545.5	63995.6
Oiled	0.15	4706.8	3471.6	41658.7	47996.2
Zinc Plated	0.18	5648.2	4165.9	49990.8	57595.8
Waxed	0.1	3137.9	2314.4	27772.8	31997.8
MoS₂	0.12	3765.5	2777.3	33327.5	38397.6
Galvanized	0.25	7844.7	5786.0	69431.5	79994.0

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 1757.73 mm² = 580,051 N

Step 2 — Torque (dry): T = 0.20 × 0.0520 m × 580,051 N = 6032.5 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.

SizeM52

Class6.8

Diameter52 mm

Pitch (coarse)5.0 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa