#10 Grade 8 Bolt Torque: 5.0 ft·lbs / 6.8 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 24 TPI

Stress area: 0.0175 in² · Proof load: 2,100 lbs · Clamp load (75%): 1,575 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	4.99	6.76	59.9	69.0
Oiled	0.15	3.74	5.07	44.9	51.7
Zinc Plated	0.18	4.49	6.09	53.9	62.1
Waxed	0.1	2.49	3.38	29.9	34.5
MoS₂	0.12	2.99	4.06	35.9	41.4
Galvanized	0.25	6.23	8.45	74.8	86.2

UNF — Fine Thread — 32 TPI

Stress area: 0.02 in² · Proof load: 2,400 lbs · Clamp load (75%): 1,800 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	5.70	7.73	68.4	78.8
Oiled	0.15	4.27	5.80	51.3	59.1
Zinc Plated	0.18	5.13	6.96	61.6	70.9
Waxed	0.1	2.85	3.86	34.2	39.4
MoS₂	0.12	3.42	4.64	41.0	47.3
Galvanized	0.25	7.12	9.66	85.5	98.5

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 2.49 ft·lbs (waxed) to 6.23 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 × 120,000 psi × 0.0175 in² = 1,575 lbs

Step 2 — Torque (dry): T = 0.20 × 0.19 in × 1,575 lbs ÷ 12 = 5.0 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 8

High-strength applications, heavy equipment, critical joints, suspension components, trailer hitches. Equivalent to ISO 10.9.

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#10

Grade8

Diameter0.19" (4.83 mm)

TPI (UNC)24

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

#10 Grade 8 Torque Spec