1-3/8" Grade 8 Torque Specification

Torque Values by Surface Condition

Stress area: 1.155 in² · Proof load: 138,600 lbs · Clamp load (75%): 103,950 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	2382.2	3229.8	28586.4	32934.9
Oiled	0.15	1786.6	2422.3	21439.2	24700.7
Zinc Plated	0.18	2144.0	2906.9	25728.0	29642.2
Waxed	0.1	1191.1	1614.9	14293.2	16467.5
MoS₂	0.12	1429.3	1937.9	17151.6	19761.2
Galvanized	0.25	2977.7	4037.2	35732.4	41168.1

Stress area: 1.315 in² · Proof load: 157,800 lbs · Clamp load (75%): 118,350 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	2712.2	3677.3	32546.4	37498.2
Oiled	0.15	2034.1	2757.9	24409.2	28122.9
Zinc Plated	0.18	2441.0	3309.6	29292.0	33748.7
Waxed	0.1	1356.1	1838.6	16273.2	18748.6
MoS₂	0.12	1627.3	2206.3	19527.6	22498.1
Galvanized	0.25	3390.2	4596.5	40682.4	46871.4

Formula: T = K × D × F

Step 1 — Clamp load: F = 0.75 × 120,000 psi × 1.155 in² = 103,950 lbs

Step 2 — Torque (dry): T = 0.20 × 1.375 in × 103,950 lbs ÷ 12 = 2382.2 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.

Size1-3/8"

Grade8

Diameter1.375" (34.92 mm)

TPI (UNC)6

Tensile150,000 psi

Yield130,000 psi

Proof120,000 psi