# 7/8-14 tap drill size

The tap drill for a 7/8-14 UNF thread is a 13/16 drill (0.8125 in, 20.64 mm). It leaves about 67 % thread. The closest metric drill is 20.6 mm, which leaves 69 % thread.

## Drill options for 7/8-14 UNF

| Drill | Inch | Thread % |
|---|---|---|
| 13/16 | 0.8125 | 67 % |
| 20.5 mm | 0.8071 | 73 % |
| 20.6 mm | 0.8110 | 69 % |
| 20.7 mm | 0.8150 | 65 % |

## 7/8-14 thread data

- Thread: 7/8-14 UNF, 14 TPI
- Major diameter: 0.8750 in (22.22 mm)
- Tap drill: 13/16 = 0.8125 in (20.64 mm)
- Thread engagement: 67 %

## Method

Thread % = TPI × (D − drill) / 0.01299 = 14 × 0.0625 / 0.01299 = 67 %.

## FAQ

**What size drill for a 7/8-14 tap?**
Use a 13/16 drill (0.8125 in, 20.64 mm). It leaves about 67 % thread.

**Can I use a metric drill for 7/8-14?**
Yes. A 20.6 mm drill gives about 69 % thread.

**How tight should a 7/8 grade 5 bolt be?**
About 474 ft-lb dry for 7/8-14 UNF.

Source page: https://machinistcharts.com/tap-drill/7-8-14/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)