# #2-56 tap drill size

The tap drill for a #2-56 UNC thread is a #50 drill (0.0700 in, 1.78 mm). It leaves about 69 % thread. The closest metric drill is 1.8 mm, which leaves 65 % thread.

## Drill options for #2-56 UNC

| Drill | Inch | Thread % |
|---|---|---|
| #50 | 0.0700 | 69 % |
| 1.7 mm | 0.0669 | 82 % |
| 1.8 mm | 0.0709 | 65 % |
| 1.9 mm | 0.0748 | 48 % |

## #2-56 thread data

- Thread: #2-56 UNC, 56 TPI
- Major diameter: 0.0860 in (2.18 mm)
- Tap drill: #50 = 0.0700 in (1.78 mm)
- Thread engagement: 69 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 56 × 0.0160 / 0.01299 = 69 %.

## FAQ

**What size drill for a #2-56 tap?**
Use a #50 drill (0.0700 in, 1.78 mm). It leaves about 69 % thread.

**Can I use a metric drill for #2-56?**
Yes. A 1.8 mm drill gives about 65 % thread.

Source page: https://machinistcharts.com/tap-drill/2-56/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)