# #12-24 tap drill size

The tap drill for a #12-24 UNC thread is a #16 drill (0.1770 in, 4.50 mm). It leaves about 72 % thread. The closest metric drill is 4.5 mm, which leaves 72 % thread.

## Drill options for #12-24 UNC

| Drill | Inch | Thread % |
|---|---|---|
| #16 | 0.1770 | 72 % |
| 4.4 mm | 0.1732 | 79 % |
| 4.5 mm | 0.1772 | 72 % |
| 4.6 mm | 0.1811 | 64 % |

## #12-24 thread data

- Thread: #12-24 UNC, 24 TPI
- Major diameter: 0.2160 in (5.49 mm)
- Tap drill: #16 = 0.1770 in (4.50 mm)
- Thread engagement: 72 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 24 × 0.0390 / 0.01299 = 72 %.

## FAQ

**What size drill for a #12-24 tap?**
Use a #16 drill (0.1770 in, 4.50 mm). It leaves about 72 % thread.

**Can I use a metric drill for #12-24?**
Yes. A 4.5 mm drill gives about 72 % thread.

Source page: https://machinistcharts.com/tap-drill/12-24/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)