1-1/8" Grade 8 Bolt Torque: 1287.6 ft·lbs

Torque Values by Surface Condition

UNC — Coarse Thread — 7 TPI

Stress area: 0.763 in² · Proof load: 91,560 lbs · Clamp load (75%): 68,670 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	1287.6	1745.8	15450.8	17801.2
Oiled	0.15	965.7	1309.3	11588.1	13350.9
Zinc Plated	0.18	1158.8	1571.1	13905.7	16021.1
Waxed	0.1	643.8	872.9	7725.4	8900.6
MoS₂	0.12	772.5	1047.4	9270.5	10680.7
Galvanized	0.25	1609.5	2182.2	19313.4	22251.5

UNF — Fine Thread — 12 TPI

Stress area: 0.856 in² · Proof load: 102,720 lbs · Clamp load (75%): 77,040 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	1444.5	1958.5	17334.0	19970.9
Oiled	0.15	1083.4	1468.9	13000.5	14978.2
Zinc Plated	0.18	1300.1	1762.7	15600.6	17973.8
Waxed	0.1	722.3	979.3	8667.0	9985.5
MoS₂	0.12	866.7	1175.1	10400.4	11982.6
Galvanized	0.25	1805.6	2448.1	21667.5	24963.7

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 643.8 ft·lbs (waxed) to 1609.5 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 × 0.763 in² = 68,670 lbs

Step 2 — Torque (dry): T = 0.20 × 1.125 in × 68,670 lbs ÷ 12 = 1287.6 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

Size1-1/8"

Grade8

Diameter1.125" (28.57 mm)

TPI (UNC)7

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

1-1/8" Grade 8 Torque Spec