M39 Grade 4.8 Torque Specification

Torque Values by Surface Condition

Stress area: 976.0 mm² · Proof load: 302,560 N · Clamp load (75%): 226,920 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	1770.0	1305.5	15665.8	18049.0
Oiled	0.15	1327.5	979.1	11749.4	13536.8
Zinc Plated	0.18	1593.0	1174.9	14099.2	16244.1
Waxed	0.1	885.0	652.7	7832.9	9024.5
MoS₂	0.12	1062.0	783.3	9399.5	10829.4
Galvanized	0.25	2212.5	1631.9	19582.3	22561.3

Stress area: 1028.4 mm² · Proof load: 318,804 N · Clamp load (75%): 239,103 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	1865.0	1375.6	16506.6	19017.8
Oiled	0.15	1398.8	1031.7	12380.4	14263.8
Zinc Plated	0.18	1678.5	1238.0	14856.0	17116.0
Waxed	0.1	932.5	687.8	8253.3	9508.9
MoS₂	0.12	1119.0	825.3	9904.0	11410.7
Galvanized	0.25	2331.3	1719.5	20633.8	23772.7

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 310 MPa × 976.0 mm² = 226,920 N

Step 2 — Torque (dry): T = 0.20 × 0.0390 m × 226,920 N = 1770.0 N·m

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

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.

SizeM39

Class4.8

Diameter39 mm

Pitch (coarse)4.0 mm

Tensile420 MPa

Yield340 MPa

Proof310 MPa