# 7/8" drill size

A 7/8 in drill is 0.8750 in (22.22 mm). It is the standard tap drill for 1-8 UNC; the nearest metric drill is 22.2 mm.

## 7/8" drill data

- Series: Fractional drill
- Decimal: 0.8750 in
- Metric: 22.22 mm (22.2250 mm exact)
- Nearest metric drill: 22.2 mm (−0.025 mm)
- Standard tap drill for: 1-8 UNC

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 22.2 mm | 0.8740 | −0.025 mm |
| 22.3 mm | 0.8780 | +0.075 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| Letter Z | Letter | 0.4130 | 10.49 |
| 55/64" | Fractional | 0.8594 | 21.83 |
| 7/8" | Fractional | 0.8750 | 22.22 |
| 57/64" | Fractional | 0.8906 | 22.62 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 1-8 UNC | 7/8 | 77 |
| M24 × 2 | 22 mm | 68 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M20 bolt | 20 mm | 2.22 mm | 1.11 mm | Normal fit (normal 22, loose 24 mm) |
| M22 bolt | 22 mm | 0.22 mm | 0.11 mm | Tighter than close fit (23 mm) |


## FAQ

**What size is a 7/8 in drill?**
A 7/8 in drill is 0.8750 in, which is 22.22 mm (22.2250 mm exactly).

**What is the metric equivalent of a 7/8 in drill?**
The nearest metric drill is 22.2 mm, 0.025 mm smaller. The other close size is 22.3 mm.

**What tap uses a 7/8 in drill?**
A 7/8 in drill is the standard tap drill for 1-8 UNC (about 77 % thread).

**What does a 7/8 in drill clear?**
It clears a M22 bolt with 0.22 mm total clearance (0.11 mm per side); for metric bolts: tighter than close fit.

Source page: https://machinistcharts.com/drill-size/7-8-inch/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)