M39 Grade 5.8 Torque Specification

Torque Values by Surface Condition

Stress area: 976.0 mm² · Proof load: 370,880 N · Clamp load (75%): 278,160 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	2169.6	1600.2	19202.6	22123.8
Oiled	0.15	1627.2	1200.2	14401.9	16592.9
Zinc Plated	0.18	1952.7	1440.2	17282.9	19912.1
Waxed	0.1	1084.8	800.1	9601.3	11061.9
MoS₂	0.12	1301.8	960.2	11521.9	13274.7
Galvanized	0.25	2712.1	2000.3	24004.1	27655.8

Stress area: 1028.4 mm² · Proof load: 390,792 N · Clamp load (75%): 293,094 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	2286.1	1686.1	20233.7	23311.8
Oiled	0.15	1714.6	1264.6	15175.5	17484.1
Zinc Plated	0.18	2057.5	1517.5	18210.4	20980.7
Waxed	0.1	1143.1	843.1	10117.3	11656.4
MoS₂	0.12	1371.7	1011.7	12140.6	13987.5
Galvanized	0.25	2857.7	2107.7	25292.8	29140.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 380 MPa × 976.0 mm² = 278,160 N

Step 2 — Torque (dry): T = 0.20 × 0.0390 m × 278,160 N = 2169.6 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.

SizeM39

Class5.8

Diameter39 mm

Pitch (coarse)4.0 mm

Tensile520 MPa

Yield420 MPa

Proof380 MPa