# 1/2 inch 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.

## 1/2 torque by thread series and SAE grade

| Thread | Grade | Dry torque (K 0.20) | Lubricated (K 0.15) | Clamp load |
|---|---|---|---|---|
| 1/2-13 UNC | Grade 2 | 49 ft-lb (66 N·m) | 37 ft-lb | 5,853 lbf |
| 1/2-13 UNC | Grade 5 | 75 ft-lb (102 N·m) | 57 ft-lb | 9,046 lbf |
| 1/2-13 UNC | Grade 8 | 106 ft-lb (144 N·m) | 80 ft-lb | 12,771 lbf |
| 1/2-20 UNF | Grade 2 | 55 ft-lb (75 N·m) | 41 ft-lb | 6,598 lbf |
| 1/2-20 UNF | Grade 5 | 85 ft-lb (115 N·m) | 64 ft-lb | 10,197 lbf |
| 1/2-20 UNF | Grade 8 | 120 ft-lb (163 N·m) | 90 ft-lb | 14,396 lbf |

Clamp load = 75 % of proof load. Method: T = K × F × d.

## 1/2 bolt data

- Threads: 1/2-13 UNC, 1/2-20 UNF
- Wrench: 3/4 in
- Tap drill: 27/64 (0.4219 in) for UNC, 29/64 (0.4531 in) for UNF

## Method

Proof strength from SAE J429 × tensile stress area As = 0.7854 × (D − 0.9743/n)² (ASME B1.1). F = 75 % of proof load. T = K × F × D with K = 0.20 dry, 0.15 lubricated.

## FAQ

**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.

Source page: https://machinistcharts.com/bolt-torque/1-2-inch/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)