M20 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 244.79 mm² · Proof load: 141,978 N · Clamp load (75%): 106,484 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	425.9	314.1	3769.5	4343.0
Oiled	0.15	319.5	235.7	2827.8	3258.0
Zinc Plated	0.18	383.3	282.7	3392.5	3908.6
Waxed	0.1	213.0	157.1	1885.2	2172.0
MoS₂	0.12	255.6	188.5	2262.3	2606.4
Galvanized	0.25	532.4	392.7	4712.1	5429.0

Stress area: 271.5 mm² · Proof load: 157,470 N · Clamp load (75%): 118,102 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	472.4	348.4	4181.1	4817.2
Oiled	0.15	354.3	261.3	3135.8	3612.9
Zinc Plated	0.18	425.2	313.6	3763.3	4335.8
Waxed	0.1	236.2	174.2	2090.5	2408.6
MoS₂	0.12	283.4	209.0	2508.3	2889.9
Galvanized	0.25	590.5	435.5	5226.4	6021.4

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 244.79 mm² = 106,484 N

Step 2 — Torque (dry): T = 0.20 × 0.0200 m × 106,484 N = 425.9 N·m

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

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.

SizeM20

Class8.8

Diameter20 mm

Pitch (coarse)2.5 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa