1/4" Grade 8 Torque Specification

Torque Values by Surface Condition

Stress area: 0.0318 in² · Proof load: 3,816 lbs · Clamp load (75%): 2,862 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	11.9	16.1	142.8	164.2
Oiled	0.15	8.9	12.1	106.8	123.4
Zinc Plated	0.18	10.7	14.5	128.4	147.9
Waxed	0.1	6.0	8.1	72.0	82.6
MoS₂	0.12	7.2	9.8	86.4	99.9
Galvanized	0.25	14.9	20.2	178.8	206.0

Stress area: 0.03637 in² · Proof load: 4,364 lbs · Clamp load (75%): 3,273 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	13.6	18.4	163.2	187.6
Oiled	0.15	10.2	13.8	122.4	140.7
Zinc Plated	0.18	12.3	16.7	147.6	170.3
Waxed	0.1	6.8	9.2	81.6	93.8
MoS₂	0.12	8.2	11.1	98.4	113.2
Galvanized	0.25	17.0	23.0	204.0	234.5

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 120,000 psi × 0.0318 in² = 2,862 lbs

Step 2 — Torque (dry): T = 0.20 × 0.25 in × 2,862 lbs ÷ 12 = 11.9 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.

Size1/4"

Grade8

Diameter0.25" (6.35 mm)

TPI (UNC)20

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi