7/8" Grade 8 Bolt Torque: 606.4 ft·lbs / 822.2 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 9 TPI

Stress area: 0.462 in² · Proof load: 55,440 lbs · Clamp load (75%): 41,580 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	606.4	822.2	7276.5	8383.4
Oiled	0.15	454.8	616.6	5457.4	6287.6
Zinc Plated	0.18	545.7	739.9	6548.8	7545.1
Waxed	0.1	303.2	411.1	3638.2	4191.7
MoS₂	0.12	363.8	493.2	4365.9	5030.1
Galvanized	0.25	758.0	1027.7	9095.6	10479.3

UNF — Fine Thread — 14 TPI

Stress area: 0.509 in² · Proof load: 61,080 lbs · Clamp load (75%): 45,810 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	668.1	905.8	8016.8	9236.3
Oiled	0.15	501.0	679.3	6012.6	6927.2
Zinc Plated	0.18	601.3	815.3	7215.1	8312.7
Waxed	0.1	334.0	452.8	4008.4	4618.1
MoS₂	0.12	400.8	543.4	4810.0	5541.8
Galvanized	0.25	835.1	1132.2	10020.9	11545.4

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 303.2 ft·lbs (waxed) to 758.0 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 × 0.462 in² = 41,580 lbs

Step 2 — Torque (dry): T = 0.20 × 0.875 in × 41,580 lbs ÷ 12 = 606.4 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

Size7/8"

Grade8

Diameter0.875" (22.22 mm)

TPI (UNC)9

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

7/8" Grade 8 Torque Spec