1-1/4" Grade 8 Bolt Torque: 1816.9 ft·lbs

Torque Values by Surface Condition

UNC — Coarse Thread — 7 TPI

Stress area: 0.969 in² · Proof load: 116,280 lbs · Clamp load (75%): 87,210 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	1816.9	2463.4	21802.5	25119.2
Oiled	0.15	1362.7	1847.6	16351.9	18839.4
Zinc Plated	0.18	1635.2	2217.0	19622.2	22607.3
Waxed	0.1	908.4	1231.6	10901.2	12559.6
MoS₂	0.12	1090.1	1478.0	13081.5	15071.5
Galvanized	0.25	2271.1	3079.2	27253.1	31399.0

UNF — Fine Thread — 12 TPI

Stress area: 1.073 in² · Proof load: 128,760 lbs · Clamp load (75%): 96,570 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	2011.9	2727.8	24142.5	27815.2
Oiled	0.15	1508.9	2045.8	18106.9	20861.4
Zinc Plated	0.18	1810.7	2455.0	21728.2	25033.7
Waxed	0.1	1005.9	1363.8	12071.2	13907.6
MoS₂	0.12	1207.1	1636.6	14485.5	16689.1
Galvanized	0.25	2514.8	3409.6	30178.1	34769.0

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 908.4 ft·lbs (waxed) to 2271.1 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 × 0.969 in² = 87,210 lbs

Step 2 — Torque (dry): T = 0.20 × 1.25 in × 87,210 lbs ÷ 12 = 1816.9 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

Size1-1/4"

Grade8

Diameter1.25" (31.75 mm)

TPI (UNC)7

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

1-1/4" Grade 8 Torque Spec