#6 Grade 5 Bolt Torque: 1.3 ft·lbs / 1.8 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 32 TPI

Stress area: 0.00909 in² · Proof load: 773 lbs · Clamp load (75%): 579 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	1.33	1.81	16.0	18.4
Oiled	0.15	1.00	1.36	12.0	13.8
Zinc Plated	0.18	1.20	1.63	14.4	16.6
Waxed	0.1	0.67	0.90	8.0	9.2
MoS₂	0.12	0.80	1.08	9.6	11.1
Galvanized	0.25	1.67	2.26	20.0	23.0

UNF — Fine Thread — 40 TPI

Stress area: 0.01015 in² · Proof load: 863 lbs · Clamp load (75%): 647 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	1.49	2.02	17.9	20.6
Oiled	0.15	1.12	1.51	13.4	15.4
Zinc Plated	0.18	1.34	1.82	16.1	18.5
Waxed	0.1	0.74	1.01	8.9	10.3
MoS₂	0.12	0.89	1.21	10.7	12.3
Galvanized	0.25	1.86	2.52	22.3	25.7

Torque by surface condition

UNC thread, ft·lbs. Values from the table above.

Same bolt, same target clamp load: thread friction alone moves the required torque from 0.67 ft·lbs (waxed) to 1.67 ft·lbs (hot-dip galvanized), 2.5× as much. Match the row to the fastener's actual finish and lubrication.

How This Value Is Calculated

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 85,000 psi × 0.00909 in² = 579 lbs

Step 2 — Torque (dry): T = 0.20 × 0.138 in × 579 lbs ÷ 12 = 1.3 ft·lbs

Proof stress per SAE J429 Table 3. Stress area per ASME B1.1. Typical K-factor, consistent with VDI 2230 friction values. SAE J429 formally covers 1/4" to 1-1/2" diameters; for numbered machine screws these figures apply the same grade proof stress (as used for Grade 5/8 machine screws sold to SAE-equivalent strength) — check the screw supplier's rating.

When to Use Grade 5

Automotive, agricultural equipment, general machinery — the most common high-strength SAE grade. Equivalent to ISO 8.8.

Important Notes

• Torque values are for standard hex bolts with unified threads per ASME B1.1. 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.
• Re-used bolts may have altered friction characteristics. Inspect threads before reuse.

Specifications

Size#6

Grade5

Diameter0.138" (3.51 mm)

TPI (UNC)32

Tensile120,000 psi

Yield92,000 psi

Proof85,000 psi

#6 Grade 5 Torque Spec