3/8" Grade 2 Bolt Torque: 20.0 ft·lbs / 27.1 N·m

Torque Values by Surface Condition

UNC — Coarse Thread — 16 TPI

Stress area: 0.0775 in² · Proof load: 4,262 lbs · Clamp load (75%): 3,197 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	20.0	27.1	239.8	276.2
Oiled	0.15	15.0	20.3	179.8	207.2
Zinc Plated	0.18	18.0	24.4	215.8	248.6
Waxed	0.1	10.0	13.6	119.9	138.1
MoS₂	0.12	12.0	16.3	143.9	165.7
Galvanized	0.25	25.0	33.9	299.7	345.3

UNF — Fine Thread — 24 TPI

Stress area: 0.0878 in² · Proof load: 4,829 lbs · Clamp load (75%): 3,622 lbs

Surface Condition	K Factor	ft·lbs	N·m	in·lbs	kgf·cm
Plain/Dry	0.2	22.6	30.6	271.6	313.0
Oiled	0.15	17.0	23.0	203.7	234.7
Zinc Plated	0.18	20.4	27.7	244.5	281.7
Waxed	0.1	11.3	15.3	135.8	156.5
MoS₂	0.12	13.6	18.4	163.0	187.8
Galvanized	0.25	28.3	38.4	339.5	391.2

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 10.0 ft·lbs (waxed) to 25.0 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 × 55,000 psi × 0.0775 in² = 3,197 lbs

Step 2 — Torque (dry): T = 0.20 × 0.375 in × 3,197 lbs ÷ 12 = 20.0 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 2

General-purpose, non-critical bolting. Most common ungraded hardware-store bolts.

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

Size3/8"

Grade2

Diameter0.375" (9.52 mm)

TPI (UNC)16

Tensile74,000 psi

Yield57,000 psi

Proof55,000 psi

3/8" Grade 2 Torque Spec