1/4 inch bolt torque

A 1/4-20 bolt takes 66 in-lb in Grade 2, 101 in Grade 5 and 143 in Grade 8, dry, at 75% of proof load; the 1/4-28 fine thread takes 75, 116 and 164. 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
1/4-20UNC (coarse)Grade 25.57.45.57.44.15.62.73.71,312 lbf5.8 kN
Grade 58.411.58.411.56.38.64.25.72,027 lbf9.0 kN
Grade 811.916.211.916.28.912.16.08.12,862 lbf12.7 kN
1/4-28UNF (fine)Grade 26.38.56.38.54.76.43.14.21,502 lbf6.7 kN
Grade 59.713.19.713.17.39.84.86.62,321 lbf10.3 kN
Grade 813.718.513.718.510.213.96.89.33,276 lbf14.6 kN

Work out 1/4 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%.

1/4-20 Grade 5, dry, plain steel

8.4ft-lb11.5N·m

101 in-lb

0102030400204060ft-lbN·m
Clamp load
2,027 lbf (9.0 kN)
Proof load
2,703 lbf

The working

  1. Tensile stress area. A = 0.7854 × (D − 0.9743 ÷ n)² = 0.7854 × (0.25 − 0.9743 ÷ 20)² = 0.0318 in²
  2. Proof load. Grade 5 proof stress is 85,000 psi, so A × stress = 2,703 lbf.
  3. Clamp load. 75% of proof load = 2,027 lbf.
  4. Torque. T = K × D × F = 0.2 × 0.25 in × 2,027 lbf = 101 in-lb ÷ 12 = 8.4 ft-lb (11.5 N·m).

Where the 1/4-20 numbers come from

The 1/4-20 UNC (coarse) thread has a tensile stress area of 0.0318 in². A Grade 8 bolt’s proof stress is 120,000 psi, so its proof load is 3,816 lbf, and 75% of that is a clamp load of 2,862 lbf.

Torque = K × D × F = 0.20 × 0.25 in × 2,862 lbf = 143 in-lb, or 11.9 ft-lb (16.2 N·m) dry. With oil (K 0.15) it’s 8.9 ft-lb (12.1 N·m).

Other sizes

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

Questions

What torque for a 1/4-20 Grade 8 bolt?

11.9 ft-lb (16.2 N·m) dry and 8.9 ft-lb (12.1 N·m) oiled, at 75% of proof load. That clamps the joint with 2,862 lbf (12.7 kN).

What torque for a 1/4-20 Grade 5 bolt?

8.4 ft-lb (11.5 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 1/4-28 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.