# #8-32 tap drill size

The tap drill for a #8-32 UNC thread is a #29 drill (0.1360 in, 3.45 mm). It leaves about 69 % thread. The closest metric drill is 3.5 mm, which leaves 65 % thread.

## Drill options for #8-32 UNC

| Drill | Inch | Thread % |
|---|---|---|
| #29 | 0.1360 | 69 % |
| 3.4 mm | 0.1339 | 74 % |
| 3.5 mm | 0.1378 | 65 % |
| 3.6 mm | 0.1417 | 55 % |

## #8-32 thread data

- Thread: #8-32 UNC, 32 TPI
- Major diameter: 0.1640 in (4.17 mm)
- Tap drill: #29 = 0.1360 in (3.45 mm)
- Thread engagement: 69 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 32 × 0.0280 / 0.01299 = 69 %.

## FAQ

**What size drill for a #8-32 tap?**
Use a #29 drill (0.1360 in, 3.45 mm). It leaves about 69 % thread.

**Can I use a metric drill for #8-32?**
Yes. A 3.5 mm drill gives about 65 % thread.

Source page: https://machinistcharts.com/tap-drill/8-32/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)