# 5/16-24 tap drill size

The tap drill for a 5/16-24 UNF thread is a I drill (0.2720 in, 6.91 mm). It leaves about 75 % thread. The closest metric drill is 6.9 mm, which leaves 75 % thread.

## Drill options for 5/16-24 UNF

| Drill | Inch | Thread % |
|---|---|---|
| I | 0.2720 | 75 % |
| 6.8 mm | 0.2677 | 83 % |
| 6.9 mm | 0.2717 | 75 % |
| 7.0 mm | 0.2756 | 68 % |

## 5/16-24 thread data

- Thread: 5/16-24 UNF, 24 TPI
- Major diameter: 0.3125 in (7.94 mm)
- Tap drill: I = 0.2720 in (6.91 mm)
- Thread engagement: 75 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 24 × 0.0405 / 0.01299 = 75 %.

## FAQ

**What size drill for a 5/16-24 tap?**
Use a I drill (0.2720 in, 6.91 mm). It leaves about 75 % thread.

**Can I use a metric drill for 5/16-24?**
Yes. A 6.9 mm drill gives about 75 % thread.

**How tight should a 5/16 grade 5 bolt be?**
About 19 ft-lb dry for 5/16-24 UNF.

Source page: https://machinistcharts.com/tap-drill/5-16-24/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)