# 51/64" drill size

A 51/64 in drill is 0.7969 in (20.24 mm). It sits between 25/32 in and 13/16 in in the fractional series; the nearest metric drill is 20.2 mm.

## 51/64" drill data

- Series: Fractional drill
- Decimal: 0.7969 in
- Metric: 20.24 mm (20.2406 mm exact)
- Nearest metric drill: 20.2 mm (−0.041 mm)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 20.2 mm | 0.7953 | −0.041 mm |
| 20.3 mm | 0.7992 | +0.059 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| Letter Z | Letter | 0.4130 | 10.49 |
| 25/32" | Fractional | 0.7812 | 19.84 |
| 51/64" | Fractional | 0.7969 | 20.24 |
| 13/16" | Fractional | 0.8125 | 20.64 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 7/8-14 UNF | 13/16 | 84 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M18 bolt | 18 mm | 2.24 mm | 1.12 mm | Normal fit (normal 20, loose 21 mm) |
| 3/4" bolt | 0.7500" | 0.0469" | 0.0234" | – |
| M20 bolt | 20 mm | 0.24 mm | 0.12 mm | Tighter than close fit (21 mm) |


## FAQ

**What size is a 51/64 in drill?**
A 51/64 in drill is 0.7969 in, which is 20.24 mm (20.2406 mm exactly).

**What is the metric equivalent of a 51/64 in drill?**
The nearest metric drill is 20.2 mm, 0.041 mm smaller. The other close size is 20.3 mm.

**What thread can I tap with a 51/64 in drill?**
It leaves about 84 % thread in 7/8-14 UNF.

**What does a 51/64 in drill clear?**
It clears a M20 bolt with 0.24 mm total clearance (0.12 mm per side); for metric bolts: tighter than close fit.

Source page: https://machinistcharts.com/drill-size/51-64-inch/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)