9/16" Grade 8 Bolt Torque: 153.6 ft·lbs / 208.3 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 12 TPI

Stress area: 0.182 in² · Proof load: 21,840 lbs · Clamp load (75%): 16,380 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	153.6	208.3	1842.8	2123.1
Oiled	0.15	115.2	156.2	1382.1	1592.3
Zinc Plated	0.18	138.2	187.4	1658.5	1910.8
Waxed	0.1	76.8	104.1	921.4	1061.5
MoS₂	0.12	92.1	124.9	1105.7	1273.8
Galvanized	0.25	192.0	260.3	2303.4	2653.8

UNF — Fine Thread — 18 TPI

Stress area: 0.203 in² · Proof load: 24,360 lbs · Clamp load (75%): 18,270 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	171.3	232.3	2055.4	2368.0
Oiled	0.15	128.5	174.2	1541.5	1776.0
Zinc Plated	0.18	154.2	209.1	1849.8	2131.2
Waxed	0.1	85.6	116.1	1027.7	1184.0
MoS₂	0.12	102.8	139.4	1233.2	1420.8
Galvanized	0.25	214.1	290.3	2569.2	2960.1

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 76.8 ft·lbs (waxed) to 192.0 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 × 0.182 in² = 16,380 lbs

Step 2 — Torque (dry): T = 0.20 × 0.5625 in × 16,380 lbs ÷ 12 = 153.6 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

Size9/16"

Grade8

Diameter0.5625" (14.29 mm)

TPI (UNC)12

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

9/16" Grade 8 Torque Spec