# 1-12 tap drill size

The tap drill for a 1-12 UNF thread is a 59/64 drill (0.9219 in, 23.42 mm). It leaves about 72 % thread. The closest metric drill is 23.4 mm, which leaves 73 % thread.

## Drill options for 1-12 UNF

| Drill | Inch | Thread % |
|---|---|---|
| 59/64 | 0.9219 | 72 % |
| 23.3 mm | 0.9173 | 76 % |
| 23.4 mm | 0.9213 | 73 % |
| 23.5 mm | 0.9252 | 69 % |

## 1-12 thread data

- Thread: 1-12 UNF, 12 TPI
- Major diameter: 1.0000 in (25.40 mm)
- Tap drill: 59/64 = 0.9219 in (23.42 mm)
- Thread engagement: 72 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 12 × 0.0781 / 0.01299 = 72 %.

## FAQ

**What size drill for a 1-12 tap?**
Use a 59/64 drill (0.9219 in, 23.42 mm). It leaves about 72 % thread.

**Can I use a metric drill for 1-12?**
Yes. A 23.4 mm drill gives about 73 % thread.

**How tight should a 1 grade 5 bolt be?**
About 704 ft-lb dry for 1-12 UNF.

Source page: https://machinistcharts.com/tap-drill/1-12/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)