# #8-36 tap drill size

The tap drill for a #8-36 UNF thread is a #29 drill (0.1360 in, 3.45 mm). It leaves about 78 % thread. The closest metric drill is 3.5 mm, which leaves 73 % thread.

## Drill options for #8-36 UNF

| Drill | Inch | Thread % |
|---|---|---|
| #29 | 0.1360 | 78 % |
| 3.4 mm | 0.1339 | 84 % |
| 3.5 mm | 0.1378 | 73 % |
| 3.6 mm | 0.1417 | 62 % |

## #8-36 thread data

- Thread: #8-36 UNF, 36 TPI
- Major diameter: 0.1640 in (4.17 mm)
- Tap drill: #29 = 0.1360 in (3.45 mm)
- Thread engagement: 78 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 36 × 0.0280 / 0.01299 = 78 %.

## FAQ

**What size drill for a #8-36 tap?**
Use a #29 drill (0.1360 in, 3.45 mm). It leaves about 78 % thread.

**Can I use a metric drill for #8-36?**
Yes. A 3.5 mm drill gives about 73 % thread.

Source page: https://machinistcharts.com/tap-drill/8-36/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)