M52 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 1757.73 mm² · Proof load: 1,019,483 N · Clamp load (75%): 764,613 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	7952.0	5865.1	70381.2	81088.1
Oiled	0.15	5964.0	4398.8	52785.9	60816.1
Zinc Plated	0.18	7156.8	5278.6	63343.0	72979.3
Waxed	0.1	3976.0	2932.5	35190.6	40544.1
MoS₂	0.12	4771.2	3519.1	42228.7	48652.9
Galvanized	0.25	9940.0	7331.4	87976.5	101360.2

Stress area: 1828.6 mm² · Proof load: 1,060,588 N · Clamp load (75%): 795,441 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	8272.6	6101.6	73218.7	84357.4
Oiled	0.15	6204.4	4576.1	54913.6	63267.5
Zinc Plated	0.18	7445.3	5491.4	65896.5	75921.2
Waxed	0.1	4136.3	3050.8	36609.4	42178.7
MoS₂	0.12	4963.6	3661.0	43931.6	50614.8
Galvanized	0.25	10340.7	7626.9	91523.0	105446.2

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 1757.73 mm² = 764,613 N

Step 2 — Torque (dry): T = 0.20 × 0.0520 m × 764,613 N = 7952.0 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.

SizeM52

Class8.8

Diameter52 mm

Pitch (coarse)5.0 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa