5/8" Grade 8 Torque Specification

Torque Values by Surface Condition

Stress area: 0.226 in² · Proof load: 27,120 lbs · Clamp load (75%): 20,340 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	211.9	287.3	2542.8	2929.7
Oiled	0.15	158.9	215.4	1906.8	2196.5
Zinc Plated	0.18	190.7	258.6	2288.4	2637.0
Waxed	0.1	105.9	143.6	1270.8	1464.3
MoS₂	0.12	127.1	172.3	1525.2	1757.0
Galvanized	0.25	264.8	359.0	3177.6	3660.8

Stress area: 0.256 in² · Proof load: 30,720 lbs · Clamp load (75%): 23,040 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	240.0	325.4	2880.0	3318.2
Oiled	0.15	180.0	244.0	2160.0	2488.1
Zinc Plated	0.18	216.0	292.9	2592.0	2986.8
Waxed	0.1	120.0	162.7	1440.0	1659.1
MoS₂	0.12	144.0	195.2	1728.0	1990.5
Galvanized	0.25	300.0	406.7	3600.0	4147.2

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 120,000 psi × 0.226 in² = 20,340 lbs

Step 2 — Torque (dry): T = 0.20 × 0.625 in × 20,340 lbs ÷ 12 = 211.9 ft·lbs

Proof stress per SAE J429 Table 3. Stress area per ASME B1.1. K-factor per VDI 2230.

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

• 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.

Size5/8"

Grade8

Diameter0.625" (15.88 mm)

TPI (UNC)11

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi