# 25/64" drill size

A 25/64 in drill is 0.3906 in (9.92 mm). It is the standard tap drill for 7/16-20 UNF; the nearest metric drill is 9.9 mm.

## 25/64" drill data

- Series: Fractional drill
- Decimal: 0.3906 in
- Metric: 9.92 mm (9.9219 mm exact)
- Nearest metric drill: 9.9 mm (−0.022 mm)
- Nearest letter drill: Letter W (0.3860 in)
- Standard tap drill for: 7/16-20 UNF

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 9.9 mm | 0.3898 | −0.022 mm |
| 10.0 mm | 0.3937 | +0.078 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| 3/8" | Fractional | 0.3750 | 9.52 |
| Letter W | Letter | 0.3860 | 9.80 |
| 25/64" | Fractional | 0.3906 | 9.92 |
| Letter X | Letter | 0.3970 | 10.08 |
| 13/32" | Fractional | 0.4062 | 10.32 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 7/16-20 UNF | 25/64 | 72 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M8 bolt | 8 mm | 1.92 mm | 0.96 mm | Normal fit (normal 9, loose 10 mm) |
| 3/8" bolt | 0.3750" | 0.0156" | 0.0078" | – |


## FAQ

**What size is a 25/64 in drill?**
A 25/64 in drill is 0.3906 in, which is 9.92 mm (9.9219 mm exactly).

**What is the metric equivalent of a 25/64 in drill?**
The nearest metric drill is 9.9 mm, 0.022 mm smaller. The other close size is 10.0 mm.

**What tap uses a 25/64 in drill?**
A 25/64 in drill is the standard tap drill for 7/16-20 UNF (about 72 % thread).

**Which number or letter drill is closest to 25/64 in?**
Letter W (0.3860 in) is the closest, 0.0046 in smaller.

**What does a 25/64 in drill clear?**
It clears a 3/8" bolt with 0.0156" total clearance (0.0078" per side).

Source page: https://machinistcharts.com/drill-size/25-64-inch/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)