# #12-28 tap drill size

The tap drill for a #12-28 UNF thread is a #14 drill (0.1820 in, 4.62 mm). It leaves about 73 % thread. The closest metric drill is 4.6 mm, which leaves 75 % thread.

## Drill options for #12-28 UNF

| Drill | Inch | Thread % |
|---|---|---|
| #14 | 0.1820 | 73 % |
| 4.5 mm | 0.1772 | 84 % |
| 4.6 mm | 0.1811 | 75 % |
| 4.7 mm | 0.1850 | 67 % |

## #12-28 thread data

- Thread: #12-28 UNF, 28 TPI
- Major diameter: 0.2160 in (5.49 mm)
- Tap drill: #14 = 0.1820 in (4.62 mm)
- Thread engagement: 73 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 28 × 0.0340 / 0.01299 = 73 %.

## FAQ

**What size drill for a #12-28 tap?**
Use a #14 drill (0.1820 in, 4.62 mm). It leaves about 73 % thread.

**Can I use a metric drill for #12-28?**
Yes. A 4.6 mm drill gives about 75 % thread.

Source page: https://machinistcharts.com/tap-drill/12-28/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)