M33 Grade 6.8 Torque Specification

Torque Values by Surface Condition

Stress area: 693.55 mm² · Proof load: 305,162 N · Clamp load (75%): 228,871 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	1510.6	1114.2	13369.9	15403.9
Oiled	0.15	1132.9	835.6	10027.0	11552.4
Zinc Plated	0.18	1359.5	1002.7	12032.6	13863.1
Waxed	0.1	755.3	557.1	6685.0	7701.9
MoS₂	0.12	906.3	668.5	8021.4	9241.7
Galvanized	0.25	1888.2	1392.7	16712.0	19254.4

Stress area: 760.85 mm² · Proof load: 334,774 N · Clamp load (75%): 251,080 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	1657.1	1222.2	14666.6	16897.8
Oiled	0.15	1242.8	916.6	10999.7	12673.1
Zinc Plated	0.18	1491.4	1100.0	13200.0	15208.1
Waxed	0.1	828.6	611.1	7333.7	8449.4
MoS₂	0.12	994.3	733.4	8800.3	10139.1
Galvanized	0.25	2071.4	1527.8	18333.4	21122.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 440 MPa × 693.55 mm² = 228,871 N

Step 2 — Torque (dry): T = 0.20 × 0.0330 m × 228,871 N = 1510.6 N·m

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

Industrial machinery, agricultural equipment, elevated load requirements

• 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.

SizeM33

Class6.8

Diameter33 mm

Pitch (coarse)3.5 mm

Tensile600 MPa

Yield480 MPa

Proof440 MPa