7/8" Grade 5 Bolt Torque: 429.5 ft·lbs / 582.3 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 9 TPI

Stress area: 0.462 in² · Proof load: 39,270 lbs · Clamp load (75%): 29,452 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	429.5	582.3	5154.2	5938.3
Oiled	0.15	322.1	436.7	3865.6	4453.7
Zinc Plated	0.18	386.6	524.2	4638.8	5344.4
Waxed	0.1	214.8	291.2	2577.1	2969.1
MoS₂	0.12	257.7	349.4	3092.5	3563.0
Galvanized	0.25	536.9	727.9	6442.7	7422.8

UNF — Fine Thread — 14 TPI

Stress area: 0.509 in² · Proof load: 43,265 lbs · Clamp load (75%): 32,449 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	473.2	641.6	5678.5	6542.4
Oiled	0.15	354.9	481.2	4258.9	4906.8
Zinc Plated	0.18	425.9	577.4	5110.7	5888.1
Waxed	0.1	236.6	320.8	2839.3	3271.2
MoS₂	0.12	283.9	384.9	3407.1	3925.4
Galvanized	0.25	591.5	802.0	7098.2	8178.0

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 214.8 ft·lbs (waxed) to 536.9 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 × 85,000 psi × 0.462 in² = 29,452 lbs

Step 2 — Torque (dry): T = 0.20 × 0.875 in × 29,452 lbs ÷ 12 = 429.5 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

Size7/8"

Grade5

Diameter0.875" (22.22 mm)

TPI (UNC)9

Tensile120,000 psi

Yield92,000 psi

Proof85,000 psi

7/8" Grade 5 Torque Spec