# Letter P drill size

A letter P drill is 0.3230 in (8.20 mm). It sits between letter O and letter Q in the letter series; the nearest metric drill is 8.2 mm.

## Letter P drill data

- Series: Letter drill
- Decimal: 0.3230 in
- Metric: 8.20 mm (8.2042 mm exact)
- Nearest metric drill: 8.2 mm (−0.004 mm)
- Nearest fractional: 21/64" (0.3281 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 8.2 mm | 0.3228 | −0.004 mm |
| 8.3 mm | 0.3268 | +0.096 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| 5/16" | Fractional | 0.3125 | 7.94 |
| Letter O | Letter | 0.3160 | 8.03 |
| Letter P | Letter | 0.3230 | 8.20 |
| 21/64" | Fractional | 0.3281 | 8.33 |
| Letter Q | Letter | 0.3320 | 8.43 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 3/8-16 UNC | 5/16 | 64 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| 5/16" bolt | 0.3125" | 0.0105" | 0.0053" | – |
| M8 bolt | 8 mm | 0.20 mm | 0.10 mm | Tighter than close fit (8.4 mm) |


## FAQ

**What size is a letter P drill?**
A letter P drill is 0.3230 in, which is 8.20 mm (8.2042 mm exactly).

**What is the metric equivalent of a letter P drill?**
The nearest metric drill is 8.2 mm, 0.004 mm smaller. The other close size is 8.3 mm.

**What thread can I tap with a letter P drill?**
It leaves about 64 % thread in 3/8-16 UNC.

**Which fractional drill is closest to letter P?**
21/64 in (0.3281 in) is the closest, 0.0051 in larger.

**What does a letter P drill clear?**
It clears a M8 bolt with 0.20 mm total clearance (0.10 mm per side); for metric bolts: tighter than close fit.

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