1-1/2" Grade 8 Bolt Torque: 3161.3 ft·lbs

Torque Values by Surface Condition

UNC — Coarse Thread — 6 TPI

Stress area: 1.405 in² · Proof load: 168,600 lbs · Clamp load (75%): 126,450 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	3161.3	4286.2	37935.0	43705.8
Oiled	0.15	2370.9	3214.5	28451.2	32779.4
Zinc Plated	0.18	2845.1	3857.4	34141.5	39335.3
Waxed	0.1	1580.6	2143.0	18967.5	21852.9
MoS₂	0.12	1896.8	2571.7	22761.0	26223.5
Galvanized	0.25	3951.6	5357.7	47418.8	54632.3

UNF — Fine Thread — 12 TPI

Stress area: 1.581 in² · Proof load: 189,720 lbs · Clamp load (75%): 142,290 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	3557.3	4823.1	42687.0	49180.7
Oiled	0.15	2667.9	3617.2	32015.2	36885.6
Zinc Plated	0.18	3201.5	4340.7	38418.3	44262.7
Waxed	0.1	1778.6	2411.5	21343.5	24590.4
MoS₂	0.12	2134.4	2893.9	25612.2	29508.4
Galvanized	0.25	4446.6	6028.8	53358.8	61475.9

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 1580.6 ft·lbs (waxed) to 3951.6 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 × 120,000 psi × 1.405 in² = 126,450 lbs

Step 2 — Torque (dry): T = 0.20 × 1.5 in × 126,450 lbs ÷ 12 = 3161.3 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

Size1-1/2"

Grade8

Diameter1.5" (38.10 mm)

TPI (UNC)6

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi

1-1/2" Grade 8 Torque Spec