#8 Grade 5 Bolt Torque: 2.4 ft·lbs / 3.3 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 32 TPI

Stress area: 0.014 in² · Proof load: 1,190 lbs · Clamp load (75%): 892 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	2.44	3.31	29.3	33.7
Oiled	0.15	1.83	2.48	22.0	25.3
Zinc Plated	0.18	2.20	2.98	26.3	30.4
Waxed	0.1	1.22	1.65	14.6	16.9
MoS₂	0.12	1.46	1.98	17.6	20.2
Galvanized	0.25	3.05	4.13	36.6	42.2

UNF — Fine Thread — 36 TPI

Stress area: 0.01474 in² · Proof load: 1,253 lbs · Clamp load (75%): 940 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	2.57	3.48	30.8	35.5
Oiled	0.15	1.93	2.61	23.1	26.6
Zinc Plated	0.18	2.31	3.13	27.7	32.0
Waxed	0.1	1.28	1.74	15.4	17.8
MoS₂	0.12	1.54	2.09	18.5	21.3
Galvanized	0.25	3.21	4.35	38.5	44.4

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 1.22 ft·lbs (waxed) to 3.05 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 × 85,000 psi × 0.014 in² = 892 lbs

Step 2 — Torque (dry): T = 0.20 × 0.164 in × 892 lbs ÷ 12 = 2.4 ft·lbs

Proof stress per SAE J429 Table 3. Stress area per ASME B1.1. Typical K-factor, consistent with VDI 2230 friction values. SAE J429 formally covers 1/4" to 1-1/2" diameters; for numbered machine screws these figures apply the same grade proof stress (as used for Grade 5/8 machine screws sold to SAE-equivalent strength) — check the screw supplier's rating.

When to Use Grade 5

Automotive, agricultural equipment, general machinery — the most common high-strength SAE grade. Equivalent to ISO 8.8.

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

Size#8

Grade5

Diameter0.164" (4.17 mm)

TPI (UNC)32

Tensile120,000 psi

Yield92,000 psi

Proof85,000 psi

#8 Grade 5 Torque Spec