M20 Grade 5.8 Torque Specification

Torque Values by Surface Condition

Stress area: 244.79 mm² · Proof load: 93,020 N · Clamp load (75%): 69,765 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	279.1	205.9	2470.2	2846.0
Oiled	0.15	209.3	154.4	1852.5	2134.3
Zinc Plated	0.18	251.2	185.3	2223.3	2561.5
Waxed	0.1	139.5	102.9	1234.7	1422.5
MoS₂	0.12	167.4	123.5	1481.6	1707.0
Galvanized	0.25	348.8	257.3	3087.1	3556.8

Stress area: 271.5 mm² · Proof load: 103,170 N · Clamp load (75%): 77,378 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	309.5	228.3	2739.3	3156.0
Oiled	0.15	232.1	171.2	2054.3	2366.8
Zinc Plated	0.18	278.6	205.5	2465.8	2840.9
Waxed	0.1	154.8	114.2	1370.1	1578.5
MoS₂	0.12	185.7	137.0	1643.6	1893.6
Galvanized	0.25	386.9	285.4	3424.4	3945.3

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 380 MPa × 244.79 mm² = 69,765 N

Step 2 — Torque (dry): T = 0.20 × 0.0200 m × 69,765 N = 279.1 N·m

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

General industrial fastening, equipment mounting, moderate structural loads

• 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

Class5.8

Diameter20 mm

Pitch (coarse)2.5 mm

Tensile520 MPa

Yield420 MPa

Proof380 MPa