1 inch bolt torque

A 1-8 bolt takes 250 ft-lb in Grade 2, 644 in Grade 5 and 909 in Grade 8, dry, at 75% of proof load; the 1-12 fine thread takes 273, 704 and 995. 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
1-8UNC (coarse)Grade 225033925033918725412516914,999 lbf66.7 kN
Grade 564487364487348365532243638,633 lbf171.8 kN
Grade 89091,2329091,23268292445561654,540 lbf242.6 kN
1-12UNF (fine)Grade 227337127337120527813718516,409 lbf73.0 kN
Grade 570495570495552871635247842,266 lbf188.0 kN
Grade 89951,3489951,3487461,01149767459,670 lbf265.4 kN

Work out 1 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%.

1-8 Grade 5, dry, plain steel

644ft-lb873N·m

020040060080004008001200ft-lbN·m
Clamp load
38,633 lbf (171.8 kN)
Proof load
51,510 lbf

The working

  1. Tensile stress area. A = 0.7854 × (D − 0.9743 ÷ n)² = 0.7854 × (1 − 0.9743 ÷ 8)² = 0.606 in²
  2. Proof load. Grade 5 proof stress is 85,000 psi, so A × stress = 51,510 lbf.
  3. Clamp load. 75% of proof load = 38,633 lbf.
  4. Torque. T = K × D × F = 0.2 × 1 in × 38,633 lbf = 7,727 in-lb ÷ 12 = 644 ft-lb (873 N·m).

Where the 1-8 numbers come from

The 1-8 UNC (coarse) thread has a tensile stress area of 0.606 in². A Grade 8 bolt’s proof stress is 120,000 psi, so its proof load is 72,720 lbf, and 75% of that is a clamp load of 54,540 lbf.

Torque = K × D × F = 0.20 × 1 in × 54,540 lbf = 10,908 in-lb, or 909 ft-lb (1,232 N·m) dry. With oil (K 0.15) it’s 682 ft-lb (924 N·m).

Other sizes

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

Questions

What torque for a 1-8 Grade 8 bolt?

909 ft-lb (1,232 N·m) dry and 682 ft-lb (924 N·m) oiled, at 75% of proof load. That clamps the joint with 54,540 lbf (242.6 kN).

What torque for a 1-8 Grade 5 bolt?

644 ft-lb (873 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 1-12 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.