# 55/64" drill size

A 55/64 in drill is 0.8594 in (21.83 mm). It sits between 27/32 in and 7/8 in in the fractional series; the nearest metric drill is 21.8 mm.

## 55/64" drill data

- Series: Fractional drill
- Decimal: 0.8594 in
- Metric: 21.83 mm (21.8281 mm exact)
- Nearest metric drill: 21.8 mm (−0.028 mm)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 21.8 mm | 0.8583 | −0.028 mm |
| 21.9 mm | 0.8622 | +0.072 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| Letter Z | Letter | 0.4130 | 10.49 |
| 27/32" | Fractional | 0.8438 | 21.43 |
| 55/64" | Fractional | 0.8594 | 21.83 |
| 7/8" | Fractional | 0.8750 | 22.22 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| M24 × 2 | 22 mm | 84 |
| M24 × 3 | 21 mm | 56 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M20 bolt | 20 mm | 1.83 mm | 0.91 mm | Close fit (close 21, normal 22 mm) |


## FAQ

**What size is a 55/64 in drill?**
A 55/64 in drill is 0.8594 in, which is 21.83 mm (21.8281 mm exactly).

**What is the metric equivalent of a 55/64 in drill?**
The nearest metric drill is 21.8 mm, 0.028 mm smaller. The other close size is 21.9 mm.

**What thread can I tap with a 55/64 in drill?**
It leaves about 84 % thread in M24 × 2 and 56 % in M24 × 3.

**What does a 55/64 in drill clear?**
It clears a M20 bolt with 1.83 mm total clearance (0.91 mm per side); for metric bolts: close fit.

Source page: https://machinistcharts.com/drill-size/55-64-inch/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)