# #10-32 tap drill size

The tap drill for a #10-32 UNF thread is a #21 drill (0.1590 in, 4.04 mm). It leaves about 76 % thread. The closest metric drill is 4.0 mm, which leaves 80 % thread.

## Drill options for #10-32 UNF

| Drill | Inch | Thread % |
|---|---|---|
| #21 | 0.1590 | 76 % |
| 3.9 mm | 0.1535 | 90 % |
| 4.0 mm | 0.1575 | 80 % |
| 4.1 mm | 0.1614 | 70 % |

## #10-32 thread data

- Thread: #10-32 UNF, 32 TPI
- Major diameter: 0.1900 in (4.83 mm)
- Tap drill: #21 = 0.1590 in (4.04 mm)
- Thread engagement: 76 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 32 × 0.0310 / 0.01299 = 76 %.

## FAQ

**What size drill for a #10-32 tap?**
Use a #21 drill (0.1590 in, 4.04 mm). It leaves about 76 % thread.

**Can I use a metric drill for #10-32?**
Yes. A 4.0 mm drill gives about 80 % thread.

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