5/8" Grade 2 Bolt Torque: 97.1 ft·lbs / 131.7 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 11 TPI

Stress area: 0.226 in² · Proof load: 12,430 lbs · Clamp load (75%): 9,322 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	97.1	131.7	1165.3	1342.6
Oiled	0.15	72.8	98.7	874.0	1006.9
Zinc Plated	0.18	87.4	118.5	1048.8	1208.3
Waxed	0.1	48.6	65.9	582.7	671.3
MoS₂	0.12	58.3	79.0	699.2	805.6
Galvanized	0.25	121.4	164.6	1456.6	1678.2

UNF — Fine Thread — 18 TPI

Stress area: 0.256 in² · Proof load: 14,080 lbs · Clamp load (75%): 10,560 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	110.0	149.1	1320.0	1520.8
Oiled	0.15	82.5	111.9	990.0	1140.6
Zinc Plated	0.18	99.0	134.2	1188.0	1368.7
Waxed	0.1	55.0	74.6	660.0	760.4
MoS₂	0.12	66.0	89.5	792.0	912.5
Galvanized	0.25	137.5	186.4	1650.0	1901.0

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 48.6 ft·lbs (waxed) to 121.4 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 × 0.226 in² = 9,322 lbs

Step 2 — Torque (dry): T = 0.20 × 0.625 in × 9,322 lbs ÷ 12 = 97.1 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 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

Size5/8"

Grade2

Diameter0.625" (15.88 mm)

TPI (UNC)11

Tensile74,000 psi

Yield57,000 psi

Proof55,000 psi

5/8" Grade 2 Torque Spec