#6 Grade 2 Bolt Torque: 0.9 ft·lbs / 1.2 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 32 TPI

Stress area: 0.00909 in² · Proof load: 500 lbs · Clamp load (75%): 375 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	0.86	1.17	10.3	11.9
Oiled	0.15	0.65	0.88	7.8	8.9
Zinc Plated	0.18	0.78	1.05	9.3	10.7
Waxed	0.1	0.43	0.58	5.2	6.0
MoS₂	0.12	0.52	0.70	6.2	7.2
Galvanized	0.25	1.08	1.46	12.9	14.9

UNF — Fine Thread — 40 TPI

Stress area: 0.01015 in² · Proof load: 558 lbs · Clamp load (75%): 419 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	0.96	1.31	11.6	13.3
Oiled	0.15	0.72	0.98	8.7	10.0
Zinc Plated	0.18	0.87	1.18	10.4	12.0
Waxed	0.1	0.48	0.65	5.8	6.7
MoS₂	0.12	0.58	0.78	6.9	8.0
Galvanized	0.25	1.20	1.63	14.4	16.6

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 0.43 ft·lbs (waxed) to 1.08 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 × 55,000 psi × 0.00909 in² = 375 lbs

Step 2 — Torque (dry): T = 0.20 × 0.138 in × 375 lbs ÷ 12 = 0.9 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 2

General-purpose, non-critical bolting. Most common ungraded hardware-store bolts.

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

Grade2

Diameter0.138" (3.51 mm)

TPI (UNC)32

Tensile74,000 psi

Yield57,000 psi

Proof55,000 psi

#6 Grade 2 Torque Spec