M20 Grade 4.8 Torque Specification

Torque Values by Surface Condition

Stress area: 244.79 mm² · Proof load: 75,885 N · Clamp load (75%): 56,914 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	227.7	167.9	2015.3	2321.9
Oiled	0.15	170.7	125.9	1510.8	1740.7
Zinc Plated	0.18	204.9	151.1	1813.5	2089.4
Waxed	0.1	113.8	83.9	1007.2	1160.4
MoS₂	0.12	136.6	100.8	1209.0	1392.9
Galvanized	0.25	284.6	209.9	2518.9	2902.1

Stress area: 271.5 mm² · Proof load: 84,165 N · Clamp load (75%): 63,124 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	252.5	186.2	2234.8	2574.8
Oiled	0.15	189.4	139.7	1676.3	1931.3
Zinc Plated	0.18	227.2	167.6	2010.9	2316.8
Waxed	0.1	126.2	93.1	1117.0	1286.9
MoS₂	0.12	151.5	111.7	1340.9	1544.9
Galvanized	0.25	315.6	232.8	2793.3	3218.2

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 310 MPa × 244.79 mm² = 56,914 N

Step 2 — Torque (dry): T = 0.20 × 0.0200 m × 56,914 N = 227.7 N·m

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

Light structural connections, furniture assembly, non-load-bearing joints

• 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

Class4.8

Diameter20 mm

Pitch (coarse)2.5 mm

Tensile420 MPa

Yield340 MPa

Proof310 MPa