# Letter W drill size

A letter W drill is 0.3860 in (9.80 mm). It sits between letter V and letter X in the letter series; the nearest metric drill is 9.8 mm.

## Letter W drill data

- Series: Letter drill
- Decimal: 0.3860 in
- Metric: 9.80 mm (9.8044 mm exact)
- Nearest metric drill: 9.8 mm (−0.004 mm)
- Nearest fractional: 25/64" (0.3906 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 9.8 mm | 0.3858 | −0.004 mm |
| 9.9 mm | 0.3898 | +0.096 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| 3/8" | Fractional | 0.3750 | 9.52 |
| Letter V | Letter | 0.3770 | 9.58 |
| Letter W | Letter | 0.3860 | 9.80 |
| 25/64" | Fractional | 0.3906 | 9.92 |
| Letter X | Letter | 0.3970 | 10.08 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 7/16-20 UNF | 25/64 | 79 |
| 7/16-14 UNC | U | 56 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M8 bolt | 8 mm | 1.80 mm | 0.90 mm | Normal fit (normal 9, loose 10 mm) |
| 3/8" bolt | 0.3750" | 0.0110" | 0.0055" | – |


## FAQ

**What size is a letter W drill?**
A letter W drill is 0.3860 in, which is 9.80 mm (9.8044 mm exactly).

**What is the metric equivalent of a letter W drill?**
The nearest metric drill is 9.8 mm, 0.004 mm smaller. The other close size is 9.9 mm.

**What thread can I tap with a letter W drill?**
It leaves about 79 % thread in 7/16-20 UNF and 56 % in 7/16-14 UNC.

**Which fractional drill is closest to letter W?**
25/64 in (0.3906 in) is the closest, 0.0046 in larger.

**What does a letter W drill clear?**
It clears a 3/8" bolt with 0.0110" total clearance (0.0055" per side).

Source page: https://machinistcharts.com/drill-size/letter-w/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)