3/8 inch bolt torque

A 3/8-16 bolt takes 20 ft-lb in Grade 2, 31 in Grade 5 and 44 in Grade 8, dry, at 75% of proof load; the 3/8-24 fine thread takes 23, 35 and 49. Oiled threads take a quarter less.

Sources checked

Torque at 75% of proof load.

Units
ThreadGradeDryK 0.20Zinc platedK 0.20OiledK 0.15WaxedK 0.10Clamp load
3/8-16UNC (coarse)Grade 220.027.120.027.115.020.310.013.53,197 lbf14.2 kN
Grade 530.941.930.941.923.231.415.420.94,941 lbf22.0 kN
Grade 843.659.143.659.132.744.321.829.66,975 lbf31.0 kN
3/8-24UNF (fine)Grade 222.630.722.630.717.023.011.315.33,622 lbf16.1 kN
Grade 535.047.435.047.426.235.617.523.75,597 lbf24.9 kN
Grade 849.467.049.467.037.050.224.733.57,902 lbf35.1 kN

Work out 3/8 inch torque

Change grade, threads or preload

Bolt standard

As received, nothing added. K 0.20 (Portland Bolt, Fastenal).

% of proof load

The published charts use 75%.

3/8-16 Grade 5, dry, plain steel

30.9ft-lb41.9N·m

0102030400204060ft-lbN·m
Clamp load
4,941 lbf (22.0 kN)
Proof load
6,588 lbf

The working

  1. Tensile stress area. A = 0.7854 × (D − 0.9743 ÷ n)² = 0.7854 × (0.375 − 0.9743 ÷ 16)² = 0.0775 in²
  2. Proof load. Grade 5 proof stress is 85,000 psi, so A × stress = 6,588 lbf.
  3. Clamp load. 75% of proof load = 4,941 lbf.
  4. Torque. T = K × D × F = 0.2 × 0.375 in × 4,941 lbf = 371 in-lb ÷ 12 = 30.9 ft-lb (41.9 N·m).

Where the 3/8-16 numbers come from

The 3/8-16 UNC (coarse) thread has a tensile stress area of 0.0775 in². A Grade 8 bolt’s proof stress is 120,000 psi, so its proof load is 9,300 lbf, and 75% of that is a clamp load of 6,975 lbf.

Torque = K × D × F = 0.20 × 0.375 in × 6,975 lbf = 523 in-lb, or 43.6 ft-lb (59.1 N·m) dry. With oil (K 0.15) it’s 32.7 ft-lb (44.3 N·m).

Other sizes

All sizes on one page: the SAE bolt torque chart.

Questions

What torque for a 3/8-16 Grade 8 bolt?

43.6 ft-lb (59.1 N·m) dry and 32.7 ft-lb (44.3 N·m) oiled, at 75% of proof load. That clamps the joint with 6,975 lbf (31.0 kN).

What torque for a 3/8-16 Grade 5 bolt?

30.9 ft-lb (41.9 N·m) dry, at 75% of proof load; a quarter less with oiled threads.

Coarse or fine thread?

Use whichever the bolt has. The fine 3/8-24 thread has a bigger stress area than the coarse one, so it takes slightly more torque for the same clamp. A thread gauge settles it.

Does this apply to wheel nuts or engine bolts?

No. Use the vehicle maker’s value for those: see lug nut torque by vehicle. These numbers are for general-purpose steel bolts where no spec exists.

Sources

  1. Portland Bolt: SAE J429: proof load, yield and tensile strength for Grades 2, 5 and 8 (checked October 14, 2026)
  2. Portland Bolt: Thread pitch chart: UNC and UNF threads per inch and tensile stress areas (checked October 14, 2026)
  3. Fastenal: Mechanical properties of inch fasteners, with UNC and UNF tensile stress areas (checked October 14, 2026)
  4. Engineering Toolbox: Threaded bolts: tensile stress area formulas for unified and ISO metric threads (checked October 14, 2026)
  5. Fastenal: Torque–tension relationship for A307 A, Grade 5, 8 and 9 coarse thread bolts (75% of proof load; K 0.15 and 0.20) (checked October 14, 2026)
  6. Portland Bolt: Bolt torque chart: T = KDP at 75% of proof load, with K for plain, waxed and galvanized bolts (checked October 14, 2026)

Spotted a number that doesn’t match your manual or a source? Tell us; corrections are logged on the sources page.