1/2" Grade 8 Bolt Torque: 106.4 ft·lbs / 144.3 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 13 TPI

Stress area: 0.1419 in² · Proof load: 17,028 lbs · Clamp load (75%): 12,771 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	106.4	144.3	1277.1	1471.4
Oiled	0.15	79.8	108.2	957.8	1103.5
Zinc Plated	0.18	95.8	129.9	1149.4	1324.2
Waxed	0.1	53.2	72.1	638.6	735.7
MoS₂	0.12	63.9	86.6	766.3	882.8
Galvanized	0.25	133.0	180.3	1596.4	1839.2

UNF — Fine Thread — 20 TPI

Stress area: 0.1599 in² · Proof load: 19,188 lbs · Clamp load (75%): 14,391 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	119.9	162.6	1439.1	1658.0
Oiled	0.15	89.9	121.9	1079.3	1243.5
Zinc Plated	0.18	107.9	146.3	1295.2	1492.2
Waxed	0.1	60.0	81.3	719.5	829.0
MoS₂	0.12	72.0	97.6	863.5	994.8
Galvanized	0.25	149.9	203.2	1798.9	2072.5

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 53.2 ft·lbs (waxed) to 133.0 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 × 0.1419 in² = 12,771 lbs

Step 2 — Torque (dry): T = 0.20 × 0.5 in × 12,771 lbs ÷ 12 = 106.4 ft·lbs

Proof stress per SAE J429 Table 3. Stress area per ASME B1.1. Typical K-factor, consistent with VDI 2230 friction values.

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

Size1/2"

Grade8

Diameter0.5" (12.70 mm)

TPI (UNC)13

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

1/2" Grade 8 Torque Spec