# 7/8 inch bolt torque

Tighten a 7/8-9 UNC grade 5 bolt to 429 ft-lb (582 N·m) with dry threads, or 322 ft-lb when lubricated. Grade 8 takes 606 ft-lb and grade 2 takes 167 ft-lb.

## 7/8 torque by thread series and SAE grade

| Thread | Grade | Dry torque (K 0.20) | Lubricated (K 0.15) | Clamp load |
|---|---|---|---|---|
| 7/8-9 UNC | Grade 2 | 167 ft-lb (226 N·m) | 125 ft-lb | 11,428 lbf |
| 7/8-9 UNC | Grade 5 | 429 ft-lb (582 N·m) | 322 ft-lb | 29,436 lbf |
| 7/8-9 UNC | Grade 8 | 606 ft-lb (822 N·m) | 455 ft-lb | 41,556 lbf |
| 7/8-14 UNF | Grade 2 | 184 ft-lb (249 N·m) | 138 ft-lb | 12,609 lbf |
| 7/8-14 UNF | Grade 5 | 474 ft-lb (642 N·m) | 355 ft-lb | 32,479 lbf |
| 7/8-14 UNF | Grade 8 | 669 ft-lb (907 N·m) | 502 ft-lb | 45,853 lbf |

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

## 7/8 bolt data

- Threads: 7/8-9 UNC, 7/8-14 UNF
- Wrench: 1-5/16 in
- Tap drill: 49/64 (0.7656 in) for UNC, 13/16 (0.8125 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 7/8 grade 5 bolt?**
About 429 ft-lb dry for 7/8-9 UNC and 474 ft-lb for 7/8-14 UNF, based on 75 % of proof load.

**What is the torque for a 7/8 grade 8 bolt?**
About 606 ft-lb dry for 7/8-9 UNC and 669 ft-lb for 7/8-14 UNF.

**What is the torque for a 7/8 grade 2 bolt?**
About 167 ft-lb dry for 7/8-9 UNC.

**What size wrench fits a 7/8 bolt?**
A standard 7/8" hex cap screw takes a 1-5/16" wrench or socket.

Source page: https://machinistcharts.com/bolt-torque/7-8-inch/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)