1/2" bolt torque

Tighten a 1/2-13 UNC grade 5 bolt to 75 ft-lb (102 N·m) with dry threads, or 57 ft-lb when lubricated. Grade 8 takes 106 ft-lb and grade 2 takes 49 ft-lb.

Calculated from SAE J429 and ASME B1.1. Updated 5 October 2026.

Grade 5, UNC, dry threads

75ft-lb

102 N·m or 905 in-lb

Grade

Thread

Threads

Unit

Torque dialBands mark each grade at dry torque

1/2" torque by thread and grade

Tap a row to show it on the dial. The unit switch above changes every value on this page.

1/2 inch bolt torque by thread series and SAE grade
Thread and grade	Dry torque	Lubricated	Clamp load	Proof load
1/2-13 UNC Grade 2	49 ft-lb	37 ft-lb	5,853 lbf	7,804 lbf
1/2-13 UNC Grade 5	75 ft-lb	57 ft-lb	9,046 lbf	12,061 lbf
1/2-13 UNC Grade 8	106 ft-lb	80 ft-lb	12,771 lbf	17,028 lbf
1/2-20 UNF Grade 2	55 ft-lb	41 ft-lb	6,598 lbf	8,797 lbf
1/2-20 UNF Grade 5	85 ft-lb	64 ft-lb	10,197 lbf	13,596 lbf
1/2-20 UNF Grade 8	120 ft-lb	90 ft-lb	14,396 lbf	19,194 lbf

Clamp load is 75 % of proof load. Dry: K = 0.20. Lubricated: K = 0.15.

1/2" at a glance

Wrench, drill and thread data for the same bolt.

1/2-13 UNC hex cap screwProportions to scale

Threads: 1/2-13 UNC
1/2-20 UNF
Stress area A_s: 0.1419 in² UNC
0.1600 in² UNF
Wrench / socket: 3/4"
Major diameter: 0.5000" 12.70 mm
Tap drill, UNC: 27/64 0.4219"
Tap drill, UNF: 29/64 0.4531"
Head markings: Grade 2 plain Grade 5 three radial lines Grade 8 six radial lines

Before you tighten

Lubricant changes the number

Oil, moly paste or anti-seize lowers the nut factor K, so the same torque produces far more clamp load. Use the lubricated value whenever the threads are oiled, or the bolt can yield.

Tighten in a star pattern

On flanges and covers, bring every bolt to about 30 %, then 70 %, then full torque, crossing the pattern each pass. Finish with one round at full torque in sequence.

Give the thread enough grip

Engage at least one diameter of thread in steel, about 1.5 diameters in cast iron and 2 diameters in aluminium, or the internal thread strips before the bolt reaches its clamp load.

These are general starting values for steel bolts in steel nuts or tapped steel. When the equipment, gasket or fastener maker publishes a torque, use theirs. Never reuse torque-to-yield bolts.

How the number is worked out

The 1/2-13 grade 5 figure, step by step.

T = K × F × d

K: 0.20, nut factor for dry plain steel
F: 9,046 lbf, 75 % of the 12,061 lbf proof load
d: 0.5000 in, nominal diameter

T = 0.20 × 9,046 × 0.5000 = 905 in-lb = 75 ft-lb

Where the inputs come from

Proof strength is taken from SAE J429: 55,000 psi for grade 2 at this size, 85,000 psi for grade 5 and 120,000 psi for grade 8. Multiply by the tensile stress area to get the proof load.

The stress area comes from ASME B1.1: A_s = 0.7854 × (D − 0.9743 / n)². Target clamp load is 75 % of proof load.

Lubricated values use K = 0.15. For other coatings or preload targets, use the torque calculator.

Other inch sizes

1/4"5/16"3/8"7/16"1/2"9/16"5/8"3/4"7/8"1"

Common questions

What is the torque for a 1/2 grade 5 bolt?

About 75 ft-lb dry for 1/2-13 UNC and 85 ft-lb for 1/2-20 UNF, based on 75 % of proof load.

What is the torque for a 1/2 grade 8 bolt?

About 106 ft-lb dry for 1/2-13 UNC and 120 ft-lb for 1/2-20 UNF.

What is the torque for a 1/2 grade 2 bolt?

About 49 ft-lb dry for 1/2-13 UNC.

What size wrench fits a 1/2 bolt?

A standard 1/2" hex cap screw takes a 3/4" wrench or socket.