# #4-48 tap drill size

The tap drill for a #4-48 UNF thread is a #42 drill (0.0935 in, 2.37 mm). It leaves about 68 % thread. The closest metric drill is 2.4 mm, which leaves 65 % thread.

## Drill options for #4-48 UNF

| Drill | Inch | Thread % |
|---|---|---|
| #42 | 0.0935 | 68 % |
| 2.3 mm | 0.0906 | 79 % |
| 2.4 mm | 0.0945 | 65 % |
| 2.5 mm | 0.0984 | 50 % |

## #4-48 thread data

- Thread: #4-48 UNF, 48 TPI
- Major diameter: 0.1120 in (2.84 mm)
- Tap drill: #42 = 0.0935 in (2.37 mm)
- Thread engagement: 68 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 48 × 0.0185 / 0.01299 = 68 %.

## FAQ

**What size drill for a #4-48 tap?**
Use a #42 drill (0.0935 in, 2.37 mm). It leaves about 68 % thread.

**Can I use a metric drill for #4-48?**
Yes. A 2.4 mm drill gives about 65 % thread.

Source page: https://machinistcharts.com/tap-drill/4-48/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)