# 3/4-10 tap drill size

The tap drill for a 3/4-10 UNC thread is a 21/32 drill (0.6563 in, 16.67 mm). It leaves about 72 % thread. The closest metric drill is 16.7 mm, which leaves 71 % thread.

## Drill options for 3/4-10 UNC

| Drill | Inch | Thread % |
|---|---|---|
| 21/32 | 0.6563 | 72 % |
| 16.6 mm | 0.6535 | 74 % |
| 16.7 mm | 0.6575 | 71 % |
| 16.8 mm | 0.6614 | 68 % |

## 3/4-10 thread data

- Thread: 3/4-10 UNC, 10 TPI
- Major diameter: 0.7500 in (19.05 mm)
- Tap drill: 21/32 = 0.6563 in (16.67 mm)
- Thread engagement: 72 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 10 × 0.0937 / 0.01299 = 72 %.

## FAQ

**What size drill for a 3/4-10 tap?**
Use a 21/32 drill (0.6563 in, 16.67 mm). It leaves about 72 % thread.

**Can I use a metric drill for 3/4-10?**
Yes. A 16.7 mm drill gives about 71 % thread.

**How tight should a 3/4 grade 5 bolt be?**
About 267 ft-lb dry for 3/4-10 UNC.

Source page: https://machinistcharts.com/tap-drill/3-4-10/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)