# Letter B drill size

A letter B drill is 0.2380 in (6.05 mm). It sits between letter A and letter C in the letter series; the nearest metric drill is 6.0 mm.

## Letter B drill data

- Series: Letter drill
- Decimal: 0.2380 in
- Metric: 6.05 mm (6.0452 mm exact)
- Nearest metric drill: 6.0 mm (−0.045 mm)
- Nearest fractional: 15/64" (0.2344 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 6.0 mm | 0.2362 | −0.045 mm |
| 6.1 mm | 0.2402 | +0.055 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| Letter A | Letter | 0.2340 | 5.94 |
| 15/64" | Fractional | 0.2344 | 5.95 |
| Letter B | Letter | 0.2380 | 6.05 |
| Letter C | Letter | 0.2420 | 6.15 |
| 1/4" | Fractional | 0.2500 | 6.35 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| #10 screw | 0.1900" | 0.0480" | 0.0240" | – |
| #12 screw | 0.2160" | 0.0220" | 0.0110" | – |
| M6 bolt | 6 mm | 0.05 mm | 0.02 mm | Tighter than close fit (6.4 mm) |


## FAQ

**What size is a letter B drill?**
A letter B drill is 0.2380 in, which is 6.05 mm (6.0452 mm exactly).

**What is the metric equivalent of a letter B drill?**
The nearest metric drill is 6.0 mm, 0.045 mm smaller. The other close size is 6.1 mm.

**Which fractional drill is closest to letter B?**
15/64 in (0.2344 in) is the closest, 0.0036 in smaller.

**What does a letter B drill clear?**
It clears a M6 bolt with 0.05 mm total clearance (0.02 mm per side); for metric bolts: tighter than close fit.

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