M33 Grade 8.8 Torque Specification

Torque Values by Surface Condition

Stress area: 693.55 mm² · Proof load: 402,259 N · Clamp load (75%): 301,694 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	1991.2	1468.6	17623.6	20304.7
Oiled	0.15	1493.4	1101.5	13217.7	15228.5
Zinc Plated	0.18	1792.1	1321.8	15861.4	18274.4
Waxed	0.1	995.6	734.3	8811.8	10152.3
MoS₂	0.12	1194.7	881.2	10574.0	12182.6
Galvanized	0.25	2489.0	1835.8	22029.5	25380.8

Stress area: 760.85 mm² · Proof load: 441,293 N · Clamp load (75%): 330,970 N

Surface Condition	K Factor	N·m	ft·lbs	in·lbs	kgf·cm
Plain/Dry	0.2	2184.4	1611.1	19333.6	22274.8
Oiled	0.15	1638.3	1208.3	14500.2	16706.1
Zinc Plated	0.18	1966.0	1450.0	17400.6	20047.7
Waxed	0.1	1092.2	805.6	9666.8	11137.4
MoS₂	0.12	1310.6	966.6	11599.8	13364.5
Galvanized	0.25	2730.5	2013.9	24167.0	27843.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 580 MPa × 693.55 mm² = 301,694 N

Step 2 — Torque (dry): T = 0.20 × 0.0330 m × 301,694 N = 1991.2 N·m

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

Automotive engines, structural connections, high-strength machinery, flanged joints — the most common high-strength grade

• 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

Class8.8

Diameter33 mm

Pitch (coarse)3.5 mm

Tensile800 MPa

Yield640 MPa

Proof580 MPa