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1/4" Grade 8 Torque Spec

Medium carbon alloy steel, quenched and tempered · Tensile 150,000 psi · Yield 130,000 psi

11.9
ft·lbs (dry)
16.1
N·m (dry)
8.9
ft·lbs (oiled)

Torque Values by Surface Condition

UNC — Coarse Thread — 20 TPI

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 16.1 143.1 164.9
Oiled 0.15 8.94 12.1 107.3 123.7
Zinc Plated 0.18 10.7 14.5 128.8 148.4
Waxed 0.1 5.96 8.08 71.6 82.4
MoS₂ 0.12 7.15 9.70 85.9 98.9
Galvanized 0.25 14.9 20.2 178.9 206.1

UNF — Fine Thread — 28 TPI

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 18.4 163.7 188.6
Oiled 0.15 10.2 13.8 122.7 141.4
Zinc Plated 0.18 12.3 16.7 147.3 169.7
Waxed 0.1 6.82 9.25 81.8 94.3
MoS₂ 0.12 8.18 11.1 98.2 113.1
Galvanized 0.25 17.0 23.0 204.6 235.7

Torque by surface condition

UNC thread, ft·lbs. Values from the table above.

Waxed (K = 0.1): 5.96 ft·lbsWaxedK = 0.15.96MoS₂ (K = 0.12): 7.15 ft·lbsMoS₂K = 0.127.15Oiled (K = 0.15): 8.94 ft·lbsOiledK = 0.158.94Zinc Plated (K = 0.18): 10.7 ft·lbsZinc PlatedK = 0.1810.7Plain/Dry (K = 0.2): 11.9 ft·lbsPlain/DryK = 0.211.9Galvanized (K = 0.25): 14.9 ft·lbsGalvanizedK = 0.2514.9

Same bolt, same target clamp load: thread friction alone moves the required torque from 5.96 ft·lbs (waxed) to 14.9 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 × 0.0318 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. 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

Size1/4"
Grade8
Diameter0.25" (6.35 mm)
TPI (UNC)20
Tensile150,000 psi
Yield130,000 psi
Proof120,000 psi

1/4" — Other Grades

Grade 2 · 5.5 ft·lbsGrade 5 · 8.4 ft·lbs

Grade 8 — Other Sizes

#6 · 1.9 ft·lbs#8 · 3.4 ft·lbs#10 · 5.0 ft·lbs5/16" · 24.6 ft·lbs3/8" · 43.6 ft·lbs1/2" · 106.4 ft·lbs3/4" · 375.8 ft·lbs1" · 909.0 ft·lbs1-1/8" · 1287.6 ft·lbs1-1/4" · 1816.9 ft·lbs1-3/8" · 2382.2 ft·lbs1-1/2" · 3161.3 ft·lbs

Explore

All 1/4" torque values → Torque calculator → ft·lbs ↔ N·m converter → Metric vs Imperial → Grade 5 vs Grade 8 → Automotive torque guide → Carbon steel torque → Nearest metric: M6 Class 10.9 →All Grade 8 sizes →Stainless bolt torque →in·lbs ↔ N·m converter →in·lbs ↔ ft·lbs converter →