5/16" Grade 5 Bolt Torque: 17.4 ft·lbs / 23.6 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 18 TPI

Stress area: 0.0524 in² · Proof load: 4,454 lbs · Clamp load (75%): 3,340 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	17.4	23.6	208.8	240.5
Oiled	0.15	13.0	17.6	156.6	180.4
Zinc Plated	0.18	15.7	21.3	187.9	216.5
Waxed	0.1	8.70	11.8	104.4	120.3
MoS₂	0.12	10.4	14.1	125.3	144.3
Galvanized	0.25	21.7	29.4	261.0	300.7

UNF — Fine Thread — 24 TPI

Stress area: 0.058 in² · Proof load: 4,930 lbs · Clamp load (75%): 3,698 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	19.3	26.2	231.1	266.2
Oiled	0.15	14.4	19.5	173.3	199.7
Zinc Plated	0.18	17.3	23.5	208.0	239.6
Waxed	0.1	9.63	13.0	115.5	133.1
MoS₂	0.12	11.6	15.7	138.7	159.7
Galvanized	0.25	24.1	32.7	288.9	332.8

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 8.70 ft·lbs (waxed) to 21.7 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 × 0.0524 in² = 3,340 lbs

Step 2 — Torque (dry): T = 0.20 × 0.3125 in × 3,340 lbs ÷ 12 = 17.4 ft·lbs

Proof stress per SAE J429 Table 3. Stress area per ASME B1.1. Typical K-factor, consistent with VDI 2230 friction values.

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

Size5/16"

Grade5

Diameter0.3125" (7.94 mm)

TPI (UNC)18

Tensile120,000 psi

Yield92,000 psi

Proof85,000 psi

5/16" Grade 5 Torque Spec