5/8" Grade 5 Bolt Torque: 150.1 ft·lbs / 203.5 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 11 TPI

Stress area: 0.226 in² · Proof load: 19,210 lbs · Clamp load (75%): 14,408 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	150.1	203.5	1800.9	2074.9
Oiled	0.15	112.6	152.7	1350.7	1556.2
Zinc Plated	0.18	135.1	183.2	1620.8	1867.4
Waxed	0.1	75.0	101.7	900.5	1037.5
MoS₂	0.12	90.1	122.2	1080.6	1244.9
Galvanized	0.25	187.6	254.4	2251.2	2593.6

UNF — Fine Thread — 18 TPI

Stress area: 0.256 in² · Proof load: 21,760 lbs · Clamp load (75%): 16,320 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	170.0	230.5	2040.0	2350.3
Oiled	0.15	127.5	172.9	1530.0	1762.8
Zinc Plated	0.18	153.0	207.4	1836.0	2115.3
Waxed	0.1	85.0	115.2	1020.0	1175.2
MoS₂	0.12	102.0	138.3	1224.0	1410.2
Galvanized	0.25	212.5	288.1	2550.0	2937.9

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 75.0 ft·lbs (waxed) to 187.6 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 × 85,000 psi × 0.226 in² = 14,408 lbs

Step 2 — Torque (dry): T = 0.20 × 0.625 in × 14,408 lbs ÷ 12 = 150.1 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 5

Automotive, agricultural equipment, general machinery — the most common high-strength SAE grade. Equivalent to ISO 8.8.

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"

Grade5

Diameter0.625" (15.88 mm)

TPI (UNC)11

Tensile120,000 psi

Yield92,000 psi

Proof85,000 psi

5/8" Grade 5 Torque Spec